Add gallery example to show usage of tile maps

examples/gallery/maps/tilemaps.py

@@ -0,0 +1,42 @@
+"""
+Tile maps
+---------
+The :meth:`pygmt.Figure.tilemap` method allows to plot
+tiles from a tile server or local file as a basemap or overlay.
+"""
+import contextily
+import pygmt
+
+fig = pygmt.Figure()
+fig.tilemap(
+    region=[-157.84, -157.8, 21.255, 21.285],
+    projection="M12c",
+    # Set level of details (0-22)
+    # Higher levels mean a zoom level closer to the Earth's
+    # surface with more tiles covering a smaller
+    # geographic area and thus more details and vice versa
+    # Please note, not all zoom levels are always available
+    zoom=14,
+    # Use tiles from OpenStreetMap tile server
+    source="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png",
+    frame="afg",
+)
+
+fig.show()
+
+###############################################################################
+# It's also possible to use tiles provided via the
+# `contextily <https://github.com/geopandas/contextily>`__
+# library. See :doc:`Contextily providers <contextily:providers_deepdive>`
+# for a list of possible tilemap options.
+
+fig = pygmt.Figure()
+fig.tilemap(
+    region=[-157.84, -157.8, 21.255, 21.285],
+    projection="M12c",
+    # Use the Stamen.Watercolor option from contextily
+    source=contextily.providers.Stamen.Watercolor,
+    frame="afg",
+)
+
+fig.show()