Create Choropleth Maps in R

USA Choropleth maps are a means of visualizing spatial data by shading or patterning areas of a map in proportion to the values of a variable. This kind of map can provide insight into how a variable is distributed across a geographic area or the level of variability within a region. 

In collaboration with Harvard researchers, the DSS team has created several choropleth maps of the contiguous USA using the R statistical programming language. These maps have helped researchers explore geographic patterning in their data. The maps are also an excellent way of presenting geospatial trends in data for publications and seminar talks.

Visualizing Probabilities or Proportions

The map illustrated below is a contrived example using a dummy variable representing probability data for each county in the contiguous USA. Probabilities less than 0.5 are shaded in increasingly deeper shades of blue, while those greater than 0.5 are shaded in increasingly deeper shades of red. In this way it is easy to see at a glance the spatial pattern of the data.

 Choropleth map of USA