choropleth_map.py

"""
Choropleth map
==============

The :meth:`pygmt.Figure.plot` method allows us to plot geographical data such as
polygons 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. You can also use a full
URL pointing to your desired data source. Then, pass the :class:`geopandas.GeoDataFrame`
as an argument to the ``data`` parameter of :meth:`pygmt.Figure.plot`, and style the
geometry using the ``pen`` parameter. To fill the polygons based on a corresponding
column you need to set ``fill="+z"`` as well as select the appropriate column using the
``aspatial`` parameter as shown in the example below.
"""

# %%
import geopandas as gpd
import pygmt

provider = "https://naciscdn.org/naturalearth"
world = gpd.read_file(f"{provider}/110m/cultural/ne_110m_admin_0_countries.zip")

# The dataset contains different attributes, here we focus on the population within
# the different countries (column "POP_EST") for the continent "Africa".
world["POP_EST"] *= 1e-6
africa = world[world["CONTINENT"] == "Africa"].copy()

fig = pygmt.Figure()
fig.basemap(region=[-19.5, 53, -37.5, 38], projection="M10c", frame="+n")

# First, we define the colormap to fill the polygons based on the "POP_EST" column.
pygmt.makecpt(cmap="SCM/acton", series=(0, 100), reverse=True)

# Next, we plot the polygons and fill them using the defined colormap. The target column
# is defined by the aspatial parameter.
fig.plot(data=africa, pen="0.8p,gray50", fill="+z", cmap=True, aspatial="Z=POP_EST")

# Add colorbar legend.
fig.colorbar(frame="x+lPopulation (millions)", position="jML+o2c/-2.5c+w5c+ef0.2c+ml")

fig.show()