Add gallery example to show usage of dcw parameter in Figure.coast

examples/gallery/maps/country_polygons.py

@@ -0,0 +1,94 @@
+"""
+Highlight country and continent polygons
+----------------------------------------
+The :meth:`pygmt.Figure.coast` method can
+highlight country polygons via the ``dcw``
+parameter. It accepts the country code, and
+can draw its borders and add a color to its landmass.
+"""
+
+# sphinx_gallery_thumbnail_number = 2
+
+
+import pygmt
+
+fig = pygmt.Figure()
+
+fig.basemap(
+    region=[-12, 32, 34, 62],
+    projection="M6c",
+    frame=True,
+)
+
+fig.coast(
+    land="gray",
+    water="white",
+    dcw=[
+        # Great Britain with seagrean land
+        "GB+gseagreen",
+        # Italy with a red border
+        "IT+p0.75p,red3",
+        # Spain with a magenta dashed border
+        "ES+p0.75p,magenta4,-",
+        # Romania with a black dotted border
+        "RO+p1p,black,.",
+        # Germany with orange land and a blue border
+        "DE+gorange+p1p,dodgerblue4",
+    ],
+)
+
+fig.show()
+
+###############################################################################
+# Entire continents can also be highlighted by adding ``"="`` in
+# front of the continent code to differentiate it from a country code.
+
+fig = pygmt.Figure()
+
+fig.coast(
+    region="d",
+    projection="H10c",
+    land="gray",
+    water="white",
+    frame="afg",
+    dcw=[
+        # Europe
+        "=EU+gseagreen",
+        # Africa
+        "=AF+gred3",
+        # North America
+        "=NA+gmagenta4",
+        # South America
+        "=SA+gorange",
+        # Asia
+        "=AS+gdodgerblue4",
+        # Oceania
+        "=OC+gtomato",
+        # Antarctica
+        "=AN+ggray30",
+    ],
+)
+
+fig.show()
+
+###############################################################################
+# If available, states/territories of a country can be highlighted, too.
+
+fig = pygmt.Figure()
+
+fig.coast(
+    region=[-130, -70, 24, 52],
+    projection="L-100/35/33/45/12c",
+    land="gray",
+    shorelines="1/0.5p",
+    borders=["1/0.8p,black", "2/0.2p,black"],
+    frame=True,
+    dcw=[
+        # Texas with orange fill
+        "US.TX+gorange",
+        # Kentucky with blue outline
+        "US.KY+p1p,blue",
+    ],
+)
+
+fig.show()