A thematic map is a geographic map that also conveys data about a theme relevant to the geographic area depicted. Thematic maps display information visually and can be used to quickly convey important points of information in a highly accessible way. There are a wide range of uses for thematic maps, ranging from epidemiology to politics, and a number of software products can be used to make these maps.
Several techniques are used in the production of thematic maps. One of the most widely known is a choropleth map, where various areas on a thematic map are colored or shaded to represent visual information. Many people have seen this type of thematic mapping on the morning after election day, when many news sources provide information about how various communities voted with a shaded map. The shades can be varied to reflect intensity, as for example in a map showing the strength of democratic or republican votes in various communities in the United States.
Proportional mapping is also used. In a proportional thematic map, geographic features may be distorted to provide information, or the symbols used on the map can vary by proportion. A map showing global energy use might scale different countries in line with the proportion of energy they use, for instance, while a map showing the size of global cities can use differently sized dots to indicate proportional size.
Dot maps, where information is presented in clusters of dots, are another type of thematic map. Visually representing information on such maps can provide information about where data points are concentrated and this information can prove very useful. Contour maps using contour lines to delineate information are another example of a thematic mapping technique. Gardening zones are often shown on a contour map to allow people to find their location and see which zone it is in.
Map design can get complicated, especially when people want to show multiple datasets to illustrate the relationship between them. Cartography software provides options for generating thematic maps and people can also draw out their own maps if they have custom needs. The ability to convey data in a simple visual form with a thematic map is valuable in a wide variety of settings, from the classroom to the boardroom, and this technique has a long history of use. Even before people fully understood the geography of the world around them, they were making thematic maps to illustrate concepts, data, and other information.