Add gallery example showing usage of line objects from a geopandas.Ge…

…oDataFrame (GenericMappingTools#1474)

Co-authored-by: Wei Ji <[email protected]>
Co-authored-by: Dongdong Tian <[email protected]>

examples/gallery/lines/roads.py

@@ -0,0 +1,43 @@
+"""
+Roads
+-----
+The :meth:`pygmt.Figure.plot` method allows us to plot geographical data such
+as lines which are stored in a :class:`geopandas.GeoDataFrame` object. Use
+:func:`geopandas.read_file` to load data from any supported OGR format such as
+a shapefile (.shp), GeoJSON (.geojson), geopackage (.gpkg), etc. Then, pass the
+:class:`geopandas.GeoDataFrame` as an argument to the ``data`` parameter in
+:meth:`pygmt.Figure.plot`, and style the geometry using the ``pen`` parameter.
+"""
+
+import geopandas as gpd
+import pygmt
+
+# Read shapefile data using geopandas
+gdf = gpd.read_file(
+    "http://www2.census.gov/geo/tiger/TIGER2015/PRISECROADS/tl_2015_15_prisecroads.zip"
+)
+# The dataset contains different road types listed in the RTTYP column,
+# here we select the following ones to plot:
+roads_common = gdf[gdf.RTTYP == "M"]  # Common name roads
+roads_state = gdf[gdf.RTTYP == "S"]  # State recognized roads
+roads_interstate = gdf[gdf.RTTYP == "I"]  # Interstate roads
+
+fig = pygmt.Figure()
+
+# Define target region around O'ahu (Hawai'i)
+region = [-158.3, -157.6, 21.2, 21.75]  # xmin, xmax, ymin, ymax
+
+title = r"Main roads of O\047ahu (Hawai\047i)"  # \047 is octal code for '
+fig.basemap(region=region, projection="M12c", frame=["af", f'WSne+t"{title}"'])
+fig.coast(land="gray", water="dodgerblue4", shorelines="1p,black")
+
+# Plot the individual road types with different pen settings and assign labels
+# which are displayed in the legend
+fig.plot(data=roads_common, pen="5p,dodgerblue", label="CommonName")
+fig.plot(data=roads_state, pen="2p,gold", label="StateRecognized")
+fig.plot(data=roads_interstate, pen="2p,red", label="Interstate")
+
+# Add legend
+fig.legend()
+
+fig.show()