A choropleth map displays divided geographical areas or regions that are coloured, shaded or patterned in relation to a data variable. It allows to study how a variable evolute along a territory.
Note that several pitfalls are commonly observed in choropleth map. The number of data point in each area remains unknown. If the variable you represent is linked to the area, you have to
normalize your variable first. (For example, you have to show a density of population and not a number of inhabitants that would be biased by the size of the area.