a map that uses lines or colors to indicate areas with similar regional aspects
Isopleth maps simplify information about a region by showing areas with continuous distribution. Isopleth maps may use lines to show areas where elevation, temperature, rainfall, or some other quality is the same; values between lines can be interpolated. Isopleths may also use color to show regions where some quality is the same; for example, a map that use shades from red to blue to indicate temperature ranges. An isopleth map differs from a choropleth map because the lines or regions are determined by the data rather than conforming to a predefined area, such as a political subdivision.