Add gallery example to show usage of tile maps

examples/gallery/maps/tilemaps.py

@@ -0,0 +1,36 @@
+"""
+Tilemaps
+--------
+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",
+    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.
+
+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()