tilemap: Use the new 'crs' parameter to simplify the tilemap function

pygmt/src/tilemap.py

@@ -9,13 +9,9 @@
 from pygmt.helpers import build_arg_list, fmt_docstring, kwargs_to_strings, use_alias
 
 try:
-    import rioxarray  # noqa: F401
     from xyzservices import TileProvider
-
-    _HAS_RIOXARRAY = True
 except ImportError:
     TileProvider = None
-    _HAS_RIOXARRAY = False
 
 
 @fmt_docstring
@@ -111,38 +107,21 @@ def tilemap(
 
     kwargs : dict
         Extra keyword arguments to pass to :meth:`pygmt.Figure.grdimage`.
-
-    Raises
-    ------
-    ImportError
-        If ``rioxarray`` is not installed. Follow
-        :doc:`install instructions for rioxarray <rioxarray:installation>`, (e.g. via
-        ``python -m pip install rioxarray``) before using this function.
     """
     kwargs = self._preprocess(**kwargs)
 
-    if not _HAS_RIOXARRAY:
-        raise ImportError(
-            "Package `rioxarray` is required to be installed to use this function. "
-            "Please use `python -m pip install rioxarray` or "
-            "`mamba install -c conda-forge rioxarray` to install the package."
-        )
-
     raster = load_tile_map(
         region=region,
         zoom=zoom,
         source=source,
         lonlat=lonlat,
+        crs="OGC:CRS84" if lonlat is True else "EPSG:3857",
         wait=wait,
         max_retries=max_retries,
         zoom_adjust=zoom_adjust,
     )
-
-    # Reproject raster from Spherical Mercator (EPSG:3857) to lonlat (OGC:CRS84) if
-    # bounding box region was provided in lonlat
-    if lonlat and raster.rio.crs == "EPSG:3857":
-        raster = raster.rio.reproject(dst_crs="OGC:CRS84")
-        raster.gmt.gtype = 1  # set to geographic type
+    if lonlat:
+        raster.gmt.gtype = 1  # Set to geographic type
 
     # Only set region if no_clip is None or False, so that plot is clipped to exact
     # bounding box region