Learning Geospatial Analysis with Python

Choropleth maps

Choropleth maps also show concentration, however, they use different shades of color to show concentration. Darker colors have higher concentration and lighter colors have lower concentration. This method is useful if related data spans multiple polygons. For example, in a worldwide population density map by country, many countries have disconnected polygons (for example, Hawaii is an island state of the US). In this example, we'll use the PIL discussed in Chapter 3, The Geospatial Technology Landscape. PIL is not purely Python but is designed specifically for Python. We'll recreate our previous dot density example as a choropleth map. We'll calculate a density ratio based on the number of people (population) per square kilometer ...