The Bay Area census tracts GeoJSON file has population data with polygon geometry. To create the first visualization we need to convert the geometry type to point:

tracts = gpd.read_file(r'tracts_bayarea.geojson')
tracts['centroids'] = tracts.centroid
tract_points = tracts
tract_points = tract_points.set_geometry('centroids')
tract_points.plot()

The output of the previous code is as follows: