This map demonstrates the use of Leaflet and Leaflet layer styling to visualize information contained in GeoJSON.
Python is used together with the Census Reporter API to get GeoJSON information for each of California's counties. A random number between 0 and 10 is then assigned to each county, and that random number is used to change the color of each county.
But why? Because the next step is to use census data, rather than random numbers, to control the style of the GeoJSON layers.
More details on the charlesreid1.com wiki.