Chloropleth map of the change in divorce rates between 1980 and 1990

 The choropleth map provides an easy way to visualize how a measurement varies across a geographic area.  
The greater the density of shading, the greater the density in reality. These maps generally use different shading, colors or placing of symbols inside specific areas on the map in order to indicate the average values of some property or quantity in those areas Examples include maps of annual rainfall, January and July temperatures, or percentages of Labour voters.
Above is a chloropleth map of the change in divorce rates between 1980 and 1990.