#!/usr/bin/env python3
"""
Axes filled with cartographic projections.
"""
import copy

import matplotlib.axis as maxis
import matplotlib.path as mpath
import matplotlib.text as mtext
import matplotlib.ticker as mticker
import numpy as np

from .. import constructor
from .. import crs as pcrs
from ..config import _parse_format, rc
from ..internals import ic  # noqa: F401
from ..internals import _not_none, dependencies, docstring, warnings
from . import plot

try:
    import cartopy.crs as ccrs
    import cartopy.feature as cfeature
    import cartopy.mpl.ticker as cticker
    from cartopy.crs import Projection
    from cartopy.mpl.geoaxes import GeoAxes as _GeoAxes
except ModuleNotFoundError:
    cfeature = cticker = ccrs = None
    _GeoAxes = Projection = object

try:
    import mpl_toolkits.basemap as mbasemap
    from mpl_toolkits.basemap import Basemap
except ModuleNotFoundError:
    mbasemap = None
    Basemap = object

__all__ = ['GeoAxes']


def _circular_boundary(N=100):
    """
    Return a circle `~matplotlib.path.Path` used as the outline for polar
    stereographic, azimuthal equidistant, Lambert conformal, and gnomonic
    projections. This was developed from `this cartopy example \
<https://scitools.org.uk/cartopy/docs/v0.15/examples/always_circular_stereo.html>`__.
    """
    theta = np.linspace(0, 2 * np.pi, N)
    center, radius = [0.5, 0.5], 0.5
    verts = np.vstack([np.sin(theta), np.cos(theta)]).T
    return mpath.Path(verts * radius + center)


class _GeoAxis(object):
    """
    Dummy axis used by longitude and latitude locators and for storing view limits on
    longitude and latitude coordinates. Modeled after how `matplotlib.ticker._DummyAxis`
    and `matplotlib.ticker.TickHelper` are used to control tick locations and labels.
    """
    # NOTE: Due to cartopy bug (https://github.com/SciTools/cartopy/issues/1564)
    # we store presistent longitude and latitude locators on axes, then *call*
    # them whenever set_extent is called and apply *fixed* locators.
    def __init__(self, axes):
        self.axes = axes
        self.major = maxis.Ticker()
        self.minor = maxis.Ticker()
        self.isDefault_majfmt = True
        self.isDefault_majloc = True
        self.isDefault_minloc = True
        self._interval = None

    def _get_extent(self):
        # Try to get extent but bail out for projections where this is
        # impossible. So far just transverse Mercator
        try:
            return self.axes.get_extent()
        except Exception:
            lon0 = self.axes._get_lon0()
            return (-180 + lon0, 180 + lon0, -90, 90)

    @staticmethod
    def _pad_ticks(ticks, vmin, vmax):
        # Wrap up to the longitude/latitude range to avoid
        # giant lists of 10,000 gridline locations.
        range_ = max(ticks) - min(ticks)
        vmin = max(vmin, ticks[0] - range_)
        vmax = min(vmax, ticks[-1] + range_)

        # Pad the reported tick range up to specified range
        step = ticks[1] - ticks[0]  # MaxNLocator/AutoMinorLocator steps are equal
        ticks_lo = np.arange(ticks[0], vmin, -step)[1:][::-1].tolist()
        ticks_hi = np.arange(ticks[-1], vmax, step)[1:].tolist()
        ticks = ticks_lo + ticks + ticks_hi
        return ticks

    @staticmethod
    def _use_dms(projection=None):
        # Return whether dms locators/formatters are available for the
        # cartopy projection and the user cartopy version. Basemap axes will
        # provide projection==None and so will always be false.
        return (
            dependencies._version_cartopy >= 0.18
            and cticker is not None
            and isinstance(projection, (ccrs._RectangularProjection, ccrs.Mercator))
        )

    def get_scale(self):
        return 'linear'

    def get_tick_space(self):
        # Just use the long-standing default of nbins=9
        return 9

    def get_major_formatter(self):
        return self.major.formatter

    def get_major_locator(self):
        return self.major.locator

    def get_minor_locator(self):
        return self.minor.locator

    def get_majorticklocs(self):
        return self._get_sanitized_ticks(self.major.locator)

    def get_minorticklocs(self):
        return self._get_sanitized_ticks(self.minor.locator)

    def set_major_formatter(self, formatter, default=False):
        # NOTE: Cartopy formatters check Formatter.axis.axes.projection and has
        # special projection-dependent behavior.
        self.major.formatter = formatter
        formatter.set_axis(self)
        self.isDefault_majfmt = default

    def set_major_locator(self, locator, default=False):
        self.major.locator = locator
        if self.major.formatter:
            self.major.formatter._set_locator(locator)
        locator.set_axis(self)
        self.isDefault_majloc = default

    def set_minor_locator(self, locator, default=False):
        self.minor.locator = locator
        locator.set_axis(self)
        self.isDefault_majfmt = default

    def set_view_interval(self, vmin, vmax):
        self._interval = (vmin, vmax)


class _LonAxis(_GeoAxis):
    """
    Axis with default longitude locator.
    """
    # NOTE: Basemap accepts tick formatters with drawmeridians(fmt=Formatter())
    # Try to use cartopy formatter if cartopy installed. Otherwise use
    # default builtin basemap formatting.
    def __init__(self, axes, projection=None):
        super().__init__(axes)
        if self._use_dms(projection):
            locator = formatter = 'dmslon'
        else:
            locator = formatter = 'deglon'
        self.set_major_formatter(constructor.Formatter(formatter), default=True)
        self.set_major_locator(constructor.Locator(locator), default=True)
        self.set_minor_locator(mticker.AutoMinorLocator(), default=True)

    def _get_sanitized_ticks(self, locator):
        # Prevent ticks from looping around
        eps = 5e-10  # more than 1e-10 because we use 1e-10 in _LongitudeLocator
        ticks = sorted(locator())
        while ticks and ticks[-1] - eps > ticks[0] + 360 + eps:  # cut off looped ticks
            ticks = ticks[:-1]

        # Append extra ticks in case longitude/latitude limits do not encompass
        # the entire view range of map, e.g. for Lambert Conformal sectors.
        # NOTE: Try to avoid making 10,000 element lists. Just wrap extra ticks
        # up to the width of *reported* longitude range.
        if isinstance(locator, (mticker.MaxNLocator, mticker.AutoMinorLocator)):
            lon0 = self.axes._get_lon0()
            ticks = self._pad_ticks(ticks, lon0 - 180 + eps, lon0 + 180 - eps)

        return ticks

    def get_view_interval(self):
        # NOTE: Proplot tries to set its *own* view intervals to avoid dateline
        # weirdness, but if cartopy.autoextent is False the interval will be
        # unset, so we are forced to use get_extent().
        interval = self._interval
        if interval is None:
            extent = self._get_extent()
            interval = extent[:2]  # longitude extents
        return interval


class _LatAxis(_GeoAxis):
    """
    Axis with default latitude locator.
    """
    def __init__(self, axes, latmax=90, projection=None):
        # NOTE: Need to pass projection because lataxis/lonaxis are
        # initialized before geoaxes is initialized, because format() needs
        # the axes and format() is called by proplot.axes.Axes.__init__()
        self._latmax = latmax
        super().__init__(axes)
        if self._use_dms(projection):
            locator = formatter = 'dmslat'
        else:
            locator = formatter = 'deglat'
        self.set_major_formatter(constructor.Formatter(formatter), default=True)
        self.set_major_locator(constructor.Locator(locator), default=True)
        self.set_minor_locator(mticker.AutoMinorLocator(), default=True)

    def _get_sanitized_ticks(self, locator):
        # Adjust latitude ticks to fix bug in some projections. Harmless for basemap.
        # NOTE: Maybe fixed by cartopy v0.18?
        eps = 5e-10
        ticks = sorted(locator())
        if ticks:
            if ticks[0] == -90:
                ticks[0] += eps
            if ticks[-1] == 90:
                ticks[-1] -= eps

        # Append extra ticks in case longitude/latitude limits do not encompass
        # the entire view range of map, e.g. for Lambert Conformal sectors.
        if isinstance(locator, (mticker.MaxNLocator, mticker.AutoMinorLocator)):
            ticks = self._pad_ticks(ticks, -90 + eps, 90 - eps)

        # Filter ticks to latmax range
        latmax = self.get_latmax()
        ticks = [l for l in ticks if -latmax <= l <= latmax]

        return ticks

    def get_latmax(self):
        return self._latmax

    def get_view_interval(self):
        interval = self._interval
        if interval is None:
            extent = self._get_extent()
            interval = extent[2:]  # latitudes
        return interval

    def set_latmax(self, latmax):
        self._latmax = latmax


class GeoAxes(plot.PlotAxes):
    """
    Axes subclass for plotting in geographic projections. Uses either cartopy
    or basemap as a "backend".
    """
    def __init__(self, *args, **kwargs):
        """
        Parameters
        ----------
        autoextent : bool, optional
            *For cartopy axes only*.
            Whether to automatically adjust map bounds based on plotted content
            or enforce global map extent. Default is :rc:`cartopy.autoextent`.
        circular : bool, optional
            *For cartopy axes only*.
            Whether to bound polar projections with circles rather than squares.
            Default is :rc:`cartopy.circular`.
        map_projection : `~mpl_toolkits.basemap.Basemap` or `~cartopy.crs.Projetion`
            The cartopy or basemap projection instance.

        Other parameters
        ----------------
        *args, **kwargs
            Passed to `~proplot.axes.Axes`.

        Note
        ----
        This makes "longitude-latitude" coordinates the default for all plotting
        commands by passing ``transform=cartopy.crs.PlateCarree()`` when cartopy is
        the backend and ``latlon=True`` when basemap is the projection. Also,
        regardless of the backend, plotting is accomplished "cartopy-style" by
        calling plotting methods on the axes instance. You should not have to
        work with the `~mpl_toolkits.basemap.Basemap` instance directly.

        See also
        --------
        proplot.ui.subplots
        proplot.axes.Axes
        proplot.axes.PlotAxes
        proplot.constructor.Proj
        """
        super().__init__(*args, **kwargs)

    def _get_lonticklocs(self, which='major'):
        """
        Retrieve longitude tick locations.
        """
        # Get tick locations from dummy axes
        # NOTE: This is workaround for: https://github.com/SciTools/cartopy/issues/1564
        # Since _axes_domain is wrong we determine tick locations ourselves with
        # more accurate extent tracked by _LatAxis and _LonAxis.
        axis = self._lonaxis
        if which == 'major':
            lines = axis.get_majorticklocs()
        else:
            lines = axis.get_minorticklocs()
        return lines

    def _get_latticklocs(self, which='major'):
        """
        Retrieve latitude tick locations.
        """
        axis = self._lataxis
        if which == 'major':
            lines = axis.get_majorticklocs()
        else:
            lines = axis.get_minorticklocs()
        return lines

    def _set_view_intervals(self, extent):
        """
        Update view intervals for lon and lat axis.
        """
        self._lonaxis.set_view_interval(*extent[:2])
        self._lataxis.set_view_interval(*extent[2:])

    @staticmethod
    def _to_label_array(labels, lon=True):
        """
        Convert labels argument to length-4 boolean array.
        """
        if labels is None:
            return [None] * 4
        which = 'lon' if lon else 'lat'

        # Parse string label indicators
        if isinstance(labels, str):
            labels = (labels,)
        array = np.atleast_1d(labels).tolist()
        if all(isinstance(_, str) for _ in array):
            bool_ = [False] * 4
            opts = ('left', 'right', 'bottom', 'top')
            for string in array:
                if string in opts:
                    string = string[0]
                elif set(string) - set('lrbt'):
                    raise ValueError(
                        f'Invalid {which}label string {string!r}. Must be one of '
                        + ', '.join(map(repr, opts))
                        + " or a string of single-letter characters like 'lr'."
                    )
                for char in string:
                    bool_['lrbt'.index(char)] = True
            array = bool_

        # Parse boolean label indicators
        if len(array) == 1:
            array.append(False)  # default is to label bottom or left
        if len(array) == 2:
            if lon:
                array = [False, False, *array]
            else:
                array = [*array, False, False]
        if len(array) != 4 or any(isinstance(_, str) for _ in array):
            raise ValueError(f'Invalid {which}label spec: {labels}.')

        return array

    @docstring._obfuscate_signature
    @docstring._snippet_manager
    def format(
        self, *,
        lonlim=None, latlim=None, boundinglat=None,
        longrid=None, latgrid=None, longridminor=None, latgridminor=None,
        lonlocator=None, lonlines=None,
        latlocator=None, latlines=None, latmax=None,
        lonminorlocator=None, lonminorlines=None,
        latminorlocator=None, latminorlines=None,
        lonlocator_kw=None, lonlines_kw=None,
        latlocator_kw=None, latlines_kw=None,
        lonminorlocator_kw=None, lonminorlines_kw=None,
        latminorlocator_kw=None, latminorlines_kw=None,
        lonformatter=None, latformatter=None,
        lonformatter_kw=None, latformatter_kw=None,
        labels=None, latlabels=None, lonlabels=None,
        loninline=None, latinline=None, inlinelabels=None, rotatelabels=None,
        labelpad=None, dms=None, nsteps=None,
        **kwargs,
    ):
        """
        Modify the longitude and latitude labels, longitude and latitude map
        limits, geographic features, and more. Additional keyword arguments are
        passed to `Axes.format` and `~proplot.config.Configurator.context`.

        Parameters
        ----------
        lonlim, latlim : 2-tuple of float, optional
            *For cartopy axes only.*
            The approximate longitude and latitude boundaries of the map,
            applied with `~cartopy.mpl.geoaxes.GeoAxes.set_extent`.
            Basemap axes extents must be declared by passing keyword arguments
            to `~proplot.constructor.Proj`.
        boundinglat : float, optional
            *For cartopy axes only.*
            The edge latitude for the circle bounding North Pole and
            South Pole-centered projections.
            Basemap bounding latitudes must be declared by passing keyword arguments
            to `~proplot.constructor.Proj`.
        longrid, latgrid : bool, optional
            Whether to draw longitude and latitude gridlines.
            Default is :rc:`grid`. Use `grid` to toggle both.
        longridminor, latgridminor : bool, optional
            Whether to draw "minor" longitude and latitude lines.
            Default is :rc:`gridminor`. Use `gridminor` to toggle both.
        lonlocator, latlocator : locator-spec, optional
            Used to determine the longitude and latitude gridline locations.
            Passed to the `~proplot.constructor.Locator` constructor. Can be
            string, float, list of float, or `matplotlib.ticker.Locator` instance.

            For basemap or cartopy < 0.18, the defaults are ``'deglon'`` and
            ``'deglat'``, which correspond to the `~proplot.ticker.LongitudeLocator`
            and `~proplot.ticker.LatitudeLocator` locators (adapted from cartopy).
            For cartopy >= 0.18, the defaults are ``'dmslon'`` and ``'dmslat'``,
            which uses the same locators with ``dms=True``. This selects gridlines
            at nice degree-minute-second intervals when the map extent is very small.
        lonlines, latlines : optional
            Aliases for `lonlocator`, `latlocator`.
        lonlocator_kw, latlocator_kw : dict-like, optional
            Keyword arguments passed to the `matplotlib.ticker.Locator` class.
        lonlines_kw, latlines_kw : optional
            Aliases for `lonlocator_kw`, `latlocator_kw`.
        lonminorlocator, latminorlocator, lonminorlines, latminorlines : optional
            As with `lonlocator` and `latlocator` but for the "minor" gridlines.
            The defaults are :rc:`grid.lonminorstep` and :rc:`grid.latminorstep`.
        lonminorlocator_kw, latminorlocator_kw, lonminorlines_kw, latminorlines_kw \
: optional
            As with `lonlocator_kw` and `latlocator_kw` but for the "minor" gridlines.
        latmax : float, optional
            The maximum absolute latitude for longitude and latitude gridlines.
            Longitude gridlines are cut off poleward of this latitude for *all*
            basemap projections and cartopy projections before cartopy 0.18.
            Default is ``80``.
        labels : bool, optional
            Sets `lonlabels` and `latlabels` to ``True``. Default is :rc:`grid.labels`.
        lonlabels, latlabels
            Whether to label longitudes and latitudes, and on which sides
            of the map. There are four different options:

            1. Boolean ``True``. Indicates the left side for latitudes,
               bottom side for longitudes.
            2. A string or tuple of strings indicating the side names, e.g.
               ``'left'`` for latitudes or ``'bottom'`` for longitudes.
            3. A string indicating the side names with single characters, e.g.
               ``'lr'`` for latitudes or ``'bt'`` for longitudes.
            4. A boolean 2-tuple indicating whether to draw labels on the
               ``(left, right)`` sides for latitudes, or ``(bottom, top)``
               sides for longitudes.
            5. A boolean 4-tuple indicating whether to draw labels on the
               ``(left, right, bottom, top)`` sides, as with the basemap
               `~mpl_toolkits.basemap.Basemap.drawmeridians` and
               `~mpl_toolkits.basemap.Basemap.drawparallels` `labels`
               keyword.

        lonformatter, latformatter : formatter-spec, optional
            Formatter used to style longitude and latitude gridline labels.
            Passed to the `~proplot.constructor.Formatter` constructor.
            Can be string, list of string, or `matplotlib.ticker.Formatter`
            instance.

            For basemap or cartopy < 0.18, the defaults are ``'deglon'`` and
            ``'deglat'``, which correspond to `~proplot.ticker.SimpleFormatter`
            presets with degree symbols and cardinal direction suffixes.
            For cartopy >= 0.18, the defaults are ``'dmslon'`` and ``'dmslat'``,
            which uses cartopy's `~cartopy.mpl.ticker.LongitudeFormatter` and
            `~cartopy.mpl.ticker.LatitudeFormatter` formatters with ``dms=True``.
            This formats gridlines that do not fall on whole degrees as "minutes"
            and "seconds" rather than decimal degrees.
        lonformatter_kw, latformatter_kw : dict-like, optional
            Keyword arguments passed to the `matplotlib.ticker.Formatter` class.
        loninline, latinline, inlinelabels : bool, optional
            *For cartopy axes only.*
            Whether to draw inline longitude and latitude gridline labels.
            Default is :rc:`grid.inlinelabels`.
        rotatelabels : bool, optional
            *For cartopy axes only.*
            Whether to rotate longitude and latitude gridline labels.
            Default is :rc:`grid.rotatelabels`.
        labelpad : unit-spec, optional
            *For cartopy axes only.*
            The padding between the map boundary and longitude and
            latitude gridline labels. Default is :rc:`grid.labelpad`.
            %(units.pt)s
        dms : bool, optional
            *For cartopy axes only.*
            Specifies whether the default locators and formatters should use
            "minutes" and "seconds" for gridline labels on small scales rather
            than decimal degrees. Setting this to ``False`` is equivalent to
            specifying ``ax.format(lonlocator='deglon', latlocator='deglon')``
            and ``ax.format(lonformatter='deglon', latformatter='deglat')``.
            Default is :rc:`grid.dmslabels`.
        nsteps : int, optional
            *For cartopy axes only.*
            The number of interpolation steps used to draw gridlines.
            Default is :rc:`grid.nsteps`.
        land, ocean, coast, rivers, lakes, borders, innerborders : bool, optional
            Toggles various geographic features. These are actually the
            :rcraw:`land`, :rcraw:`ocean`, :rcraw:`coast`, :rcraw:`rivers`,
            :rcraw:`lakes`, :rcraw:`borders`, and :rcraw:`innerborders`
            settings passed to `~proplot.config.Configurator.context`.
            The style can be modified using additional `rc` settings.

            For example, to change :rcraw:`land.color`, use
            ``ax.format(landcolor='green')``, and to change :rcraw:`land.zorder`,
            use ``ax.format(landzorder=4)``.
        reso : {'lo', 'med', 'hi', 'x-hi', 'xx-hi'}, optional
            *For cartopy axes only.*
            The resolution of geographic features. For basemap axes, this must
            be passed to `~proplot.constructor.Proj`.

        Other parameters
        ----------------
        %(axes.format)s
        %(figure.format)s
        %(axes.rc)s

        See also
        --------
        proplot.axes.Axes.format
        proplot.config.Configurator.context
        """
        # Initialize map boundary
        # WARNING: Normal workflow is Axes.format() does 'universal' tasks including
        # updating the map boundary (in the future may also handle gridlines). However
        # drawing gridlines before basemap map boundary will call set_axes_limits()
        # which initializes a boundary hidden from external access. So we must call
        # it here. Must do this between matplotlib.Axes.__init__() and Axes.format().
        if self._name == 'basemap' and self._map_boundary is None:
            if self.projection.projection in self._proj_non_rectangular:
                patch = self.projection.drawmapboundary(ax=self)
                self._map_boundary = patch
            else:
                self.projection.set_axes_limits(self)  # initialize aspect ratio
                self._map_boundary = object()  # sentinel

        # Initiate context block
        rc_kw, rc_mode, kwargs = _parse_format(**kwargs)
        with rc.context(rc_kw, mode=rc_mode):
            # Label toggles
            labels = _not_none(labels, rc.find('grid.labels', context=True))
            lonlabels = _not_none(lonlabels, labels)
            latlabels = _not_none(latlabels, labels)
            lonarray = self._to_label_array(lonlabels, lon=True)
            latarray = self._to_label_array(latlabels, lon=False)

            # Update 'maximum latitude'
            latmax = _not_none(latmax, rc.find('grid.latmax', context=True))
            if latmax is not None:
                self._lataxis.set_latmax(latmax)

            # Update major locators
            lonlocator = _not_none(lonlocator=lonlocator, lonlines=lonlines)
            latlocator = _not_none(latlocator=latlocator, latlines=latlines)
            if lonlocator is not None:
                lonlocator_kw = _not_none(
                    lonlocator_kw=lonlocator_kw, lonlines_kw=lonlines_kw, default={},
                )
                locator = constructor.Locator(lonlocator, **lonlocator_kw)
                self._lonaxis.set_major_locator(locator)
            if latlocator is not None:
                latlocator_kw = _not_none(
                    latlocator_kw=latlocator_kw, latlines_kw=latlines_kw, default={},
                )
                locator = constructor.Locator(latlocator, **latlocator_kw)
                self._lataxis.set_major_locator(locator)

            # Update minor locators
            lonminorlocator = _not_none(
                lonminorlocator=lonminorlocator, lonminorlines=lonminorlines
            )
            latminorlocator = _not_none(
                latminorlocator=latminorlocator, latminorlines=latminorlines
            )
            if lonminorlocator is not None:
                lonminorlocator_kw = _not_none(
                    lonminorlocator_kw=lonminorlocator_kw,
                    lonminorlines_kw=lonminorlines_kw,
                    default={},
                )
                locator = constructor.Locator(lonminorlocator, **lonminorlocator_kw)
                self._lonaxis.set_minor_locator(locator)
            if latminorlocator is not None:
                latminorlocator_kw = _not_none(
                    latminorlocator_kw=latminorlocator_kw,
                    latminorlines_kw=latminorlines_kw,
                    default={},
                )
                locator = constructor.Locator(latminorlocator, **latminorlocator_kw)
                self._lataxis.set_minor_locator(locator)

            # Update formatters
            loninline = _not_none(loninline, inlinelabels, rc.find('grid.inlinelabels', context=True))  # noqa: E501
            latinline = _not_none(latinline, inlinelabels, rc.find('grid.inlinelabels', context=True))  # noqa: E501
            rotatelabels = _not_none(rotatelabels, rc.find('grid.rotatelabels', context=True))  # noqa: E501
            labelpad = _not_none(labelpad, rc.find('grid.labelpad', context=True))
            dms = _not_none(dms, rc.find('grid.dmslabels', context=True))
            nsteps = _not_none(nsteps, rc.find('grid.nsteps', context=True))
            if lonformatter is not None:
                lonformatter_kw = lonformatter_kw or {}
                formatter = constructor.Formatter(lonformatter, **lonformatter_kw)
                self._lonaxis.set_major_formatter(formatter)
            if latformatter is not None:
                latformatter_kw = latformatter_kw or {}
                formatter = constructor.Formatter(latformatter, **latformatter_kw)
                self._lataxis.set_major_formatter(formatter)
            if dms is not None:  # harmless if these are not GeoLocators
                self._lonaxis.get_major_formatter()._dms = dms
                self._lataxis.get_major_formatter()._dms = dms
                self._lonaxis.get_major_locator()._dms = dms
                self._lataxis.get_major_locator()._dms = dms

            # Apply worker functions
            self._update_extent(lonlim=lonlim, latlim=latlim, boundinglat=boundinglat)
            self._update_features()
            self._update_major_gridlines(
                longrid=longrid, latgrid=latgrid,  # gridline toggles
                lonarray=lonarray, latarray=latarray,  # label toggles
                loninline=loninline, latinline=latinline, rotatelabels=rotatelabels,
                labelpad=labelpad, nsteps=nsteps,
            )
            self._update_minor_gridlines(
                longrid=longridminor, latgrid=latgridminor, nsteps=nsteps,
            )

        # Parent format method
        super().format(rc_kw=rc_kw, rc_mode=rc_mode, **kwargs)

    @property
    def projection(self):
        """
        The `~cartopy.crs.Projection` or `~mpl_toolkits.basemap.Basemap`
        instance associated with this axes.
        """
        return self._map_projection

    @projection.setter
    def projection(self, map_projection):
        cls = self._proj_class
        if not isinstance(map_projection, cls):
            raise ValueError(f'Projection must be a {cls} instance.')
        self._map_projection = map_projection


class _CartopyAxes(GeoAxes, _GeoAxes):
    """
    Axes subclass for plotting cartopy projections.
    """
    _name = 'cartopy'
    _name_aliases = ('geo', 'geographic')  # default 'geographic' axes
    _proj_class = Projection
    _proj_north = (
        pcrs.NorthPolarStereo,
        pcrs.NorthPolarGnomonic,
        pcrs.NorthPolarAzimuthalEquidistant,
        pcrs.NorthPolarLambertAzimuthalEqualArea,
    )
    _proj_south = (
        pcrs.SouthPolarStereo,
        pcrs.SouthPolarGnomonic,
        pcrs.SouthPolarAzimuthalEquidistant,
        pcrs.SouthPolarLambertAzimuthalEqualArea
    )
    _proj_polar = _proj_north + _proj_south

    def __init__(
        self, *args, autoextent=None, circular=None, map_projection=None, **kwargs
    ):
        """
        Other parameters
        ----------------
        **kwargs
            Passed to `GeoAxes`.
        """
        # GeoAxes initialization. Note that critical attributes like
        # outline_patch needed by _format_apply are added before it is called.
        # NOTE: Initial extent is configured in _update_extent
        import cartopy  # noqa: F401 verify package is available
        if not isinstance(map_projection, ccrs.Projection):
            raise ValueError(
                'Cartopy axes require map_projection=cartopy.crs.Projection.'
            )
        latmax = 90
        boundinglat = None
        polar = isinstance(map_projection, self._proj_polar)
        if polar:
            latmax = 80
            boundinglat = 0
            if isinstance(map_projection, pcrs.NorthPolarGnomonic):
                boundinglat = 30  # *default* bounding latitudes
            elif isinstance(map_projection, pcrs.SouthPolarGnomonic):
                boundinglat = -30

        # Initialize axes
        self._boundinglat = None  # NOTE: must start at None so _update_extent acts
        self._map_projection = map_projection  # cartopy also does this
        self._gridlines_major = None
        self._gridlines_minor = None
        self._lonaxis = _LonAxis(self, projection=map_projection)
        self._lataxis = _LatAxis(self, latmax=latmax, projection=map_projection)
        super().__init__(*args, map_projection=map_projection, **kwargs)

        # Apply circular map boundary for polar projections. Apply default
        # global extent for other projections.
        # NOTE: This has to come after initialization so set_extent and set_global
        # can do their things. This also updates _LatAxis and _LonAxis.
        # NOTE: Use set_global rather than _update_extent() manually in case projection
        # extent cannot be global.
        auto = _not_none(autoextent, rc['cartopy.autoextent'])
        circular = _not_none(circular, rc['cartopy.circular'])
        if polar and circular and hasattr(self, 'set_boundary'):
            self.set_boundary(_circular_boundary(), transform=self.transAxes)
        if auto:
            self._set_view_intervals(self._get_global_extent())
        elif polar:
            self._update_extent(boundinglat=boundinglat)
        else:
            self.set_global()

        # Zero out ticks to prevent extra label offset
        for axis in (self.xaxis, self.yaxis):
            axis.set_tick_params(which='both', size=0)

    def _apply_axis_sharing(self):  # noqa: U100
        """
        No-op for now. In future will hide labels on certain subplots.
        """
        pass

    def _get_global_extent(self):
        """
        Return the global extent with meridian properly shifted.
        """
        lon0 = self._get_lon0()
        return [-180 + lon0, 180 + lon0, -90, 90]

    def _get_lon0(self):
        """
        Get the central longitude. Default is ``0``.
        """
        return self.projection.proj4_params.get('lon_0', 0)

    def _init_gridlines(self):
        """
        Create monkey patched "major" and "minor" gridliners managed by ProPlot.
        """
        # Cartopy 0.18 monkey patch. This fixes issue where we get overlapping
        # gridlines on dateline. See the "nx -= 1" line in Gridliner._draw_gridliner
        # TODO: Submit cartopy PR. This is awful but necessary for quite a while if
        # the time between v0.17 and v0.18 is any indication.
        def _draw_gridliner(self, *args, **kwargs):
            result = type(self)._draw_gridliner(self, *args, **kwargs)
            if dependencies._version_cartopy >= 0.18:
                lon_lim, _ = self._axes_domain()
                if abs(np.diff(lon_lim)) == abs(np.diff(self.crs.x_limits)):
                    for collection in self.xline_artists:
                        if not getattr(collection, '_cartopy_fix', False):
                            collection.get_paths().pop(-1)
                            collection._cartopy_fix = True
            return result

        # Cartopy < 0.18 monkey patch. This is part of filtering valid label coordinates
        # to values between lon_0 - 180 and lon_0 + 180.
        def _axes_domain(self, *args, **kwargs):
            x_range, y_range = type(self)._axes_domain(self, *args, **kwargs)
            if dependencies._version_cartopy < 0.18:
                lon_0 = self.axes.projection.proj4_params.get('lon_0', 0)
                x_range = np.asarray(x_range) + lon_0
            return x_range, y_range

        # Cartopy < 0.18 gridliner method monkey patch. Always print number in range
        # (180W, 180E). We choose #4 of the following choices 3 choices (see Issue #78):
        # 1. lonlines go from -180 to 180, but get double 180 labels at dateline
        # 2. lonlines go from -180 to e.g. 150, but no lines from 150 to dateline
        # 3. lonlines go from lon_0 - 180 to lon_0 + 180 mod 360, but results
        #    in non-monotonic array causing double gridlines east of dateline
        # 4. lonlines go from lon_0 - 180 to lon_0 + 180 monotonic, but prevents
        #    labels from being drawn outside of range (-180, 180)
        def _add_gridline_label(self, value, axis, upper_end):
            if dependencies._version_cartopy < 0.18:
                if axis == 'x':
                    value = (value + 180) % 360 - 180
            return type(self)._add_gridline_label(self, value, axis, upper_end)
        gl = self.gridlines(crs=ccrs.PlateCarree())
        gl._draw_gridliner = _draw_gridliner.__get__(gl)  # apply monkey patch
        gl._axes_domain = _axes_domain.__get__(gl)
        gl._add_gridline_label = _add_gridline_label.__get__(gl)
        gl.xlines = gl.ylines = False
        self._toggle_gridliner_labels(gl, False, False, False, False)
        return gl

    @staticmethod
    def _toggle_gridliner_labels(gl, left, right, bottom, top):
        """
        Toggle gridliner labels across different cartopy versions.
        """
        if dependencies._version_cartopy >= 0.18:  # cartopy >= 0.18
            left_labels = 'left_labels'
            right_labels = 'right_labels'
            bottom_labels = 'bottom_labels'
            top_labels = 'top_labels'
        else:  # cartopy < 0.18
            left_labels = 'ylabels_left'
            right_labels = 'ylabels_right'
            bottom_labels = 'xlabels_bottom'
            top_labels = 'xlabels_top'
        if left is not None:
            setattr(gl, left_labels, left)
        if right is not None:
            setattr(gl, right_labels, right)
        if bottom is not None:
            setattr(gl, bottom_labels, bottom)
        if top is not None:
            setattr(gl, top_labels, top)

    def _update_extent(self, lonlim=None, latlim=None, boundinglat=None):
        """
        Set the projection extent.
        """
        # Projection extent
        # NOTE: Lon axis and lat axis extents are updated by set_extent.
        # WARNING: The set_extent method tries to set a *rectangle* between the *4*
        # (x, y) coordinate pairs (each corner), so something like (-180, 180, -90, 90)
        # will result in *line*, causing error! We correct this here.
        eps = 1e-10  # bug with full -180, 180 range when lon_0 != 0
        lon0 = self._get_lon0()
        proj = type(self.projection).__name__
        north = isinstance(self.projection, self._proj_north)
        south = isinstance(self.projection, self._proj_south)
        extent = None
        if north or south:
            if lonlim is not None or latlim is not None:
                warnings._warn_proplot(
                    f'{proj!r} extent is controlled by "boundinglat", '
                    f'ignoring lonlim={lonlim!r} and latlim={latlim!r}.'
                )
            if boundinglat is not None and boundinglat != self._boundinglat:
                lat0 = 90 if north else -90
                lon0 = self._get_lon0()
                extent = [lon0 - 180 + eps, lon0 + 180 - eps, boundinglat, lat0]
                self.set_extent(extent, crs=ccrs.PlateCarree())
                self._boundinglat = boundinglat

        # Rectangular extent
        else:
            if boundinglat is not None:
                warnings._warn_proplot(
                    f'{proj!r} extent is controlled by "lonlim" and "latlim", '
                    f'ignoring boundinglat={boundinglat!r}.'
                )
            if lonlim is not None or latlim is not None:
                lonlim = list(lonlim or [None, None])
                latlim = list(latlim or [None, None])
                if lonlim[0] is None:
                    lonlim[0] = lon0 - 180
                if lonlim[1] is None:
                    lonlim[1] = lon0 + 180
                lonlim[0] += eps
                if latlim[0] is None:
                    latlim[0] = -90
                if latlim[1] is None:
                    latlim[1] = 90
                extent = lonlim + latlim
                self.set_extent(extent, crs=ccrs.PlateCarree())

    def _update_background(self, **kwargs):
        """
        Update the map boundary patches. This is called in `Axes.format`.
        """
        # TODO: Understand issue where setting global linewidth puts map boundary on
        # top of land patches, but setting linewidth with format() (even with separate
        # format() calls) puts map boundary underneath. Zorder seems to be totally
        # ignored and using spines vs. patch makes no difference.
        # NOTE: outline_patch is redundant, use background_patch instead
        context = rc._context_mode == 2
        kw_face, kw_edge = self._get_background_props(context=context, **kwargs)
        kw_face['linewidth'] = 0
        kw_edge['facecolor'] = 'none'
        if dependencies._version_cartopy >= 0.18:
            self.patch.update(kw_face)
            self.spines['geo'].update(kw_edge)
        else:
            self.background_patch.update(kw_face)
            self.outline_patch.update(kw_edge)

    def _update_features(self):
        """
        Update geographic features.
        """
        # NOTE: The e.g. cfeature.COASTLINE features are just for convenience,
        # lo res versions. Use NaturalEarthFeature instead.
        # WARNING: Seems cartopy features cannot be updated! Updating _kwargs
        # attribute does *nothing*.
        reso = rc['reso']  # resolution cannot be changed after feature created
        try:
            reso = constructor.RESOS_CARTOPY[reso]
        except KeyError:
            raise ValueError(
                f'Invalid resolution {reso!r}. Options are: '
                + ', '.join(map(repr, constructor.RESOS_CARTOPY)) + '.'
            )
        for name, args in constructor.FEATURES_CARTOPY.items():
            # Draw feature or toggle feature off
            b = rc.find(name, context=True)
            attr = f'_{name}_feature'
            feat = getattr(self, attr, None)
            drawn = feat is not None  # if exists, apply *updated* settings
            if b is not None:
                if not b:
                    if drawn:  # toggle existing feature off
                        feat.set_visible(False)
                else:
                    if not drawn:
                        feat = cfeature.NaturalEarthFeature(*args, reso)
                        feat = self.add_feature(feat)  # convert to FeatureArtist

            # Update artist attributes (FeatureArtist._kwargs used back to v0.5).
            # For 'lines', need to specify edgecolor and facecolor
            # See: https://github.com/SciTools/cartopy/issues/803
            if feat is not None:
                kw = rc.category(name, context=drawn)
                if name in ('coast', 'rivers', 'borders', 'innerborders'):
                    kw.update({'edgecolor': kw.pop('color'), 'facecolor': 'none'})
                else:
                    kw.update({'linewidth': 0})
                if 'zorder' in kw:
                    # NOTE: Necessary to update zorder directly because _kwargs
                    # attributes are not applied until draw()... at which point
                    # matplotlib is drawing in the order based on the *old* zorder.
                    feat.set_zorder(kw['zorder'])
                if hasattr(feat, '_kwargs'):
                    feat._kwargs.update(kw)

    def _update_gridlines(
        self, gl, which='major', longrid=None, latgrid=None, nsteps=None,
    ):
        """
        Update gridliner object with axis locators, and toggle gridlines on and off.
        """
        # Update gridliner collection properties
        # WARNING: Here we use native matplotlib 'grid' rc param for geographic
        # gridlines. If rc mode is 1 (first format call) use context=False
        ctx = rc._context_mode == 2
        kwlines = self._get_gridline_props(which=which, context=ctx)
        kwtext = self._get_ticklabel_props(context=ctx)
        gl.collection_kwargs.update(kwlines)
        gl.xlabel_style.update(kwtext)
        gl.ylabel_style.update(kwtext)

        # Apply tick locations from dummy _LonAxis and _LatAxis axes
        # NOTE: This will re-apply existing gridline locations if unchanged.
        if nsteps is not None:
            gl.n_steps = nsteps
        latmax = self._lataxis.get_latmax()
        if hasattr(gl, 'ylim'):  # cartopy > 0.19
            gl.ylim = (-latmax, latmax)
        longrid = self._get_gridline_toggle(longrid, axis='x', which=which, context=ctx)
        if longrid is not None:
            gl.xlines = longrid
        latgrid = self._get_gridline_toggle(latgrid, axis='y', which=which, context=ctx)
        if latgrid is not None:
            gl.ylines = latgrid
        lonlines = self._get_lonticklocs(which=which)
        latlines = self._get_latticklocs(which=which)
        lonlines = (np.asarray(lonlines) + 180) % 360 - 180  # specific to _CartopyAxes
        gl.xlocator = mticker.FixedLocator(lonlines)
        gl.ylocator = mticker.FixedLocator(latlines)

    def _update_major_gridlines(
        self,
        longrid=None, latgrid=None,
        lonarray=None, latarray=None,
        loninline=None, latinline=None, labelpad=None,
        rotatelabels=None, nsteps=None,
    ):
        """
        Update major gridlines.
        """
        # Update gridline locations and style
        if self._gridlines_major is None:
            self._gridlines_major = self._init_gridlines()
        gl = self._gridlines_major
        self._update_gridlines(
            gl, which='major', longrid=longrid, latgrid=latgrid, nsteps=nsteps,
        )

        # Update gridline label parameters
        # NOTE: The 'xpadding' and 'ypadding' props were introduced in v0.16
        # with default 5 points, then set to default None in v0.18.
        # TODO: Cartopy has had two formatters for a while but we use newer one
        # https://github.com/SciTools/cartopy/pull/1066
        if labelpad is not None:
            gl.xpadding = gl.ypadding = labelpad
        if loninline is not None:
            gl.x_inline = loninline
        if latinline is not None:
            gl.y_inline = latinline
        if rotatelabels is not None:
            gl.rotate_labels = rotatelabels  # ignored in cartopy <0.18

        # Gridline label formatters
        lonaxis = self._lonaxis
        lataxis = self._lataxis
        gl.xformatter = lonaxis.get_major_formatter()
        gl.yformatter = lataxis.get_major_formatter()

        # Gridline label toggling
        # Issue warning instead of error!
        if (
            dependencies._version_cartopy < 0.18
            and not isinstance(self.projection, (ccrs.Mercator, ccrs.PlateCarree))
        ):
            if any(latarray):
                warnings._warn_proplot(
                    'Cannot add gridline labels to cartopy '
                    f'{type(self.projection).__name__} projection.'
                )
                latarray = [0] * 4
            if any(lonarray):
                warnings._warn_proplot(
                    'Cannot add gridline labels to cartopy '
                    f'{type(self.projection).__name__} projection.'
                )
                lonarray = [0] * 4
        self._toggle_gridliner_labels(gl, *latarray[:2], *lonarray[2:])

    def _update_minor_gridlines(self, longrid=None, latgrid=None, nsteps=None):
        """
        Update minor gridlines.
        """
        if self._gridlines_minor is None:
            self._gridlines_minor = self._init_gridlines()
        gl = self._gridlines_minor
        self._update_gridlines(
            gl, which='minor', longrid=longrid, latgrid=latgrid, nsteps=nsteps,
        )

    def get_extent(self, crs=None):
        # Get extent and try to repair longitude bounds.
        if crs is None:
            crs = ccrs.PlateCarree()
        extent = super().get_extent(crs=crs)
        if isinstance(crs, ccrs.PlateCarree):
            if np.isclose(extent[0], -180) and np.isclose(extent[-1], 180):
                # Repair longitude bounds to reflect dateline position
                # NOTE: This is critical so we can prevent duplicate gridlines
                # on dateline. See _update_gridlines.
                lon0 = self._get_lon0()
                extent[:2] = [lon0 - 180, lon0 + 180]
        return extent

    def get_tightbbox(self, renderer, *args, **kwargs):
        # Perform extra post-processing steps
        # For now this just draws the gridliners
        self._apply_axis_sharing()
        if self.get_autoscale_on() and self.ignore_existing_data_limits:
            self.autoscale_view()

        # Adjust location
        if dependencies._version_cartopy >= 0.18:
            self.patch._adjust_location()  # this does the below steps
        elif (
            getattr(self.background_patch, 'reclip', None)
            and hasattr(self.background_patch, 'orig_path')
        ):
            clipped_path = self.background_patch.orig_path.clip_to_bbox(self.viewLim)
            self.outline_patch._path = clipped_path
            self.background_patch._path = clipped_path

        # Apply aspect
        self.apply_aspect()
        for gl in self._gridliners:
            if dependencies._version_cartopy >= 0.18:
                gl._draw_gridliner(renderer=renderer)
            else:
                gl._draw_gridliner(background_patch=self.background_patch)

        # Remove gridliners
        if dependencies._version_cartopy < 0.18:
            self._gridliners = []

        return super().get_tightbbox(renderer, *args, **kwargs)

    def set_extent(self, extent, crs=None):
        # Fix paths, so axes tight bounding box gets correct box! From this issue:
        # https://github.com/SciTools/cartopy/issues/1207#issuecomment-439975083
        # Also record the requested longitude latitude extent so we can use these
        # values for LongitudeLocator and LatitudeLocator. Otherwise if longitude
        # extent is across dateline LongitudeLocator fails because get_extent()
        # reports -180 to 180: https://github.com/SciTools/cartopy/issues/1564
        # NOTE: This is *also* not perfect because if set_extent() was called
        # and extent crosses map boundary of rectangular projection, the *actual*
        # resulting extent is the opposite. But that means user has messed up anyway
        # so probably doesn't matter if gridlines are also wrong.
        if crs is None:
            crs = ccrs.PlateCarree()
        if isinstance(crs, ccrs.PlateCarree):
            self._set_view_intervals(extent)
            with rc.context(mode=2):  # do not reset gridline properties!
                self._update_gridlines(self._gridlines_major, which='major')
                self._update_gridlines(self._gridlines_minor, which='minor')
            if dependencies._version_cartopy < 0.18:
                clipped_path = self.outline_patch.orig_path.clip_to_bbox(self.viewLim)
                self.outline_patch._path = clipped_path
                self.background_patch._path = clipped_path
        return super().set_extent(extent, crs=crs)

    def set_global(self):
        # Set up "global" extent and update _LatAxis and _LonAxis view intervals
        result = super().set_global()
        self._set_view_intervals(self._get_global_extent())
        return result


class _BasemapAxes(GeoAxes):
    """
    Axes subclass for plotting basemap projections.
    """
    _name = 'basemap'
    _proj_class = Basemap
    _proj_north = ('npaeqd', 'nplaea', 'npstere')
    _proj_south = ('spaeqd', 'splaea', 'spstere')
    _proj_polar = _proj_north + _proj_south
    _proj_non_rectangular = _proj_polar + (  # do not use axes spines as boundaries
        'ortho', 'geos', 'nsper',
        'moll', 'hammer', 'robin',
        'eck4', 'kav7', 'mbtfpq',
        'sinu', 'vandg',
    )

    def __init__(self, *args, map_projection=None, **kwargs):
        """
        Other parameters
        ----------------
        **kwargs
            Passed to `GeoAxes`.
        """
        # First assign projection and set axis bounds for locators
        # WARNING: Unlike cartopy projections basemaps cannot normally be reused.
        # To make syntax similar we make a copy.
        # WARNING: Investigated whether Basemap.__init__() could be called
        # twice with updated proj kwargs to modify map bounds after creation
        # and python immmediately crashes. Do not try again.
        import mpl_toolkits.basemap  # noqa: F401 verify package is available
        if not isinstance(map_projection, mbasemap.Basemap):
            raise ValueError(
                'Basemap axes require map_projection=mpl_toolkits.basemap.Basemap.'
            )
        map_projection = self._map_projection = copy.copy(map_projection)
        lon0 = self._get_lon0()
        if map_projection.projection in self._proj_polar:
            latmax = 80  # default latmax for gridlines
            extent = [-180 + lon0, 180 + lon0]
            bound = getattr(map_projection, 'boundinglat', 0)
            north = map_projection.projection in self._proj_north
            extent.extend([bound, 90] if north else [-90, bound])
        else:
            latmax = 90
            attrs = ('lonmin', 'lonmax', 'latmin', 'latmax')
            extent = [getattr(map_projection, attr, None) for attr in attrs]
            if any(_ is None for _ in extent):
                extent = [180 - lon0, 180 + lon0, -90, 90]  # fallback

        # Initialize axes
        self._map_boundary = None  # see format()
        self._has_recurred = False  # use this to override plotting methods
        self._lonlines_major = None  # store gridliner objects this way
        self._lonlines_minor = None
        self._latlines_major = None
        self._latlines_minor = None
        self._lonarray = 4 * [False]  # cached label toggles
        self._latarray = 4 * [False]  # cached label toggles
        self._lonaxis = _LonAxis(self)
        self._lataxis = _LatAxis(self, latmax=latmax)
        self._set_view_intervals(extent)
        super().__init__(*args, **kwargs)

    def _get_lon0(self):
        """
        Get the central longitude.
        """
        return getattr(self.projection, 'projparams', {}).get('lon_0', 0)

    @staticmethod
    def _iter_gridlines(dict_):
        """
        Iterate over longitude latitude lines.
        """
        dict_ = dict_ or {}
        for pi in dict_.values():
            for pj in pi:
                for obj in pj:
                    yield obj

    def _update_extent(self, lonlim=None, latlim=None, boundinglat=None):
        """
        No-op. Map bounds cannot be changed in basemap.
        """
        if lonlim is not None or latlim is not None or boundinglat is not None:
            warnings._warn_proplot(
                f'Got lonlim={lonlim!r}, latlim={latlim!r}, '
                f'boundinglat={boundinglat!r}, but you cannot "zoom into" a '
                'basemap projection after creating it. Add any of the following '
                "keyword args in your call to pplt.Proj('name', basemap=True, ...): "
                "'boundinglat', 'llcrnrlon', 'llcrnrlat', "
                "'urcrnrlon', 'urcrnrlat', 'llcrnrx', 'llcrnry', "
                "'urcrnrx', 'urcrnry', 'width', or 'height'."
            )

    def _update_background(self, **kwargs):
        """
        Update the map boundary patches. This is called in `Axes.format`.
        """
        # Non-rectangular projections
        # WARNING: Map boundary must be drawn before all other tasks. See __init__.
        # WARNING: With clipping on boundary lines are clipped by the axes bbox.
        ctx = rc._context_mode == 2
        if self.projection.projection in self._proj_non_rectangular:
            self.patch.set_facecolor('none')  # make sure main patch is hidden
            kw_face, kw_edge = self._get_background_props(context=ctx, **kwargs)
            kw = {**kw_face, **kw_edge, 'rasterized': False, 'clip_on': False}
            self._map_boundary.update(kw)
        # Rectangular projections
        else:
            kw_face, kw_edge = self._get_background_props(context=ctx, **kwargs)
            self.patch.update({**kw_face, 'edgecolor': 'none'})
            for spine in self.spines.values():
                spine.update(kw_edge)

    def _update_features(self):
        """
        Update geographic features.
        """
        # NOTE: Also notable are drawcounties, blumarble, drawlsmask,
        # shadedrelief, and etopo methods.
        for name, method in constructor.FEATURES_BASEMAP.items():
            # Draw feature or toggle on and off
            b = rc.find(name, context=True)
            attr = f'_{name}_feature'
            feat = getattr(self, attr, None)
            drawn = feat is not None  # if exists, apply *updated* settings
            if b is not None:
                if not b:
                    if drawn:  # toggle existing feature off
                        for obj in feat:
                            feat.set_visible(False)
                else:
                    if not drawn:
                        feat = getattr(self.projection, method)(ax=self)
                    if not isinstance(feat, (list, tuple)):  # list of artists?
                        feat = (feat,)
                    setattr(self, attr, feat)

            # Update settings
            if feat is not None:
                kw = rc.category(name, context=drawn)
                for obj in feat:
                    obj.update(kw)

    def _update_gridlines(
        self, which='major', longrid=None, latgrid=None, lonarray=None, latarray=None,
    ):
        """
        Apply changes to the basemap axes. Extra kwargs are used
        to update the proj4 params.
        """
        latmax = self._lataxis.get_latmax()
        for axis, name, grid, array, method in zip(
            ('x', 'y'),
            ('lon', 'lat'),
            (longrid, latgrid),
            (lonarray, latarray),
            ('drawmeridians', 'drawparallels'),
        ):
            # Correct lonarray and latarray label toggles by changing from lrbt to lrtb.
            # Then update the cahced toggle array. This lets us change gridline locs
            # while preserving the label toggle setting from a previous format() call.
            ctx = rc._context_mode == 2
            grid = self._get_gridline_toggle(grid, axis=axis, which=which, context=ctx)
            axis = getattr(self, f'_{name}axis')
            if which == 'major':
                bools = getattr(self, f'_{name}array')
            else:
                bools = 4 * [False]
            array = [*array[:2], *array[2:][::-1]]  # flip to lrtb
            for i, b in enumerate(array):
                if b is not None:
                    bools[i] = b  # update toggles

            # Get gridlines
            # NOTE: This may re-apply existing gridlines.
            lines = list(getattr(self, f'_get_{name}ticklocs')(which=which))
            if name == 'lon' and np.isclose(lines[0] + 360, lines[-1]):
                lines = lines[:-1]  # prevent double labels

            # Figure out whether we have to redraw meridians/parallels
            # NOTE: Always update minor gridlines if major locator also changed
            attr = f'_{name}lines_{which}'
            objs = getattr(self, attr)  # dictionary of previous objects
            attrs = ['isDefault_majloc']  # always check this one
            attrs.append('isDefault_majfmt' if which == 'major' else 'isDefault_minloc')
            rebuild = lines and (
                not objs
                or any(_ is not None for _ in array)  # user-input or initial toggles
                or any(not getattr(axis, attr) for attr in attrs)  # none tracked yet
            )
            if rebuild and objs and grid is None:  # get *previous* toggle state
                grid = all(obj.get_visible() for obj in self._iter_gridlines(objs))

            # Draw or redraw meridian or parallel lines
            # Also mark formatters and locators as 'default'
            if rebuild:
                kwdraw = {}
                formatter = axis.get_major_formatter()
                if formatter is not None:  # use functional formatter
                    kwdraw['fmt'] = formatter
                for obj in self._iter_gridlines(objs):
                    obj.set_visible(False)
                objs = getattr(self.projection, method)(
                    lines, ax=self, latmax=latmax, labels=bools, **kwdraw
                )
                setattr(self, attr, objs)

            # Update gridline settings
            # WARNING: Here we use native matplotlib 'grid' rc param for geographic
            # gridlines. If rc mode is 1 (first format call) use context=False
            ctx = not rebuild and rc._context_mode == 2
            kwlines = self._get_gridline_props(which=which, context=ctx)
            kwtext = self._get_ticklabel_props(context=ctx)
            for obj in self._iter_gridlines(objs):
                if isinstance(obj, mtext.Text):
                    obj.update(kwtext)
                else:
                    obj.update(kwlines)

            # Toggle existing gridlines on and off
            if grid is not None:
                for obj in self._iter_gridlines(objs):
                    obj.set_visible(grid)

    def _update_major_gridlines(
        self,
        longrid=None, latgrid=None, lonarray=None, latarray=None,
        loninline=None, latinline=None, rotatelabels=None, labelpad=None, nsteps=None,
    ):
        """
        Update major gridlines.
        """
        loninline, latinline, labelpad, rotatelabels, nsteps  # avoid U100 error
        self._update_gridlines(
            which='major',
            longrid=longrid, latgrid=latgrid, lonarray=lonarray, latarray=latarray,
        )

    def _update_minor_gridlines(self, longrid=None, latgrid=None, nsteps=None):
        """
        Update minor gridlines.
        """
        # Update gridline locations
        nsteps  # avoid U100 error
        array = [None] * 4  # NOTE: must be None not False (see _update_gridlines)
        self._update_gridlines(
            which='minor',
            longrid=longrid, latgrid=latgrid, lonarray=array, latarray=array,
        )
        # Set isDefault_majloc, etc. to True for both axes
        # NOTE: This cannot be done inside _update_gridlines or minor gridlines
        # will not update to reflect new major gridline locations.
        for axis in (self._lonaxis, self._lataxis):
            axis.isDefault_majfmt = True
            axis.isDefault_majloc = True
            axis.isDefault_minloc = True
