shows differences between areas by using colors or shading to represent distinct categories of qualities (such as vegetation type) or quantities (such as the percentage graduating from high school, population density, or birthrate).
A choropleth map is a map which shows regions or areas which have the same characteristics. Each area (county) is shaded according to the data. Technically, a choropleth map is based on a stepped statistical surface.
A choropleth map (Greek Ï‡Ï‰ÏÎ±, area, region + Ï€Î»Î·Î¸Î±Î¯Î½Ï‰ multiply) is a map in which areas are shaded or patterned in proportion to the measurement of the statistical variable being displayed on the map, such as population density or per-capita income. It provides an easy way to visualize how a measurement varies across a geographic area. Choropleth is often misspelled as chloropleth -- with an extra L -- because it is mistakenly assumed that the name of the map refers to its use of color.