A thematic map focuses on a specific theme or variable, commonly using geographic data such as coastlines, boundaries, and places as points of reference for the variable being mapped. These maps provide specific information about particular locations or areas (proportional symbol mapping and choropleth maps) and information about spatial patterns (isarithmic and raster maps). The following sections illustrate the R code you need to produce these maps, with a final section devoted to the visualization of vector fields.
8.1 Proportional Symbol Mapping
The proportional symbol technique uses symbols of different sizes to represent data associated with areas or point locations, with circles being the most ...