A thematic map is a map that emphasizes a particular theme or special topic such as the average distribution of rainfall in an area. They are different from general reference maps because they do not just show natural features like rivers, cities, political subdivisions and highways. Instead, if these items are on a thematic map, they are simply used as reference points to enhance one's understanding of the map's theme and purpose.
Normally however, all thematic maps use maps with coastlines, city locations and political boundaries as their base maps. The map's specific theme is then layered onto this base map via different mapping programs and technologies like a geographic information system (GIS).
When cartographers design thematic maps today, there are several important things to consider. The most significant though is the map's audience. This is important because it helps determine what items should be included on the thematic map as reference points in addition to the map's theme. A map being made for a political scientist for example would need to have political boundaries, whereas one for a biologist might instead need contours showing elevation.
The sources of a thematic map's data are also important and should be carefully considered. Cartographers must find accurate, recent and reliable sources of information in a wide range of subjects- from environmental features to demographic data to make the best possible maps.