Maps are a means of communication. If a person has gone to the trouble of making a map, presumeably this cartographer is trying to communicate something about a place. Probably, he or she wants some audience to understand something specific, and to treat this understanding with some sense of credibility. Despite the complicated data and analysis that may underly it, the best map is one that communicates its specific message to the viewer with a minimum of effort. This page covers some of the essential properties of maps that communicate effectively and with credibility.
Some of the principles discussed on this page apply to all maps or documents that include maps. Some of them apply only to certain types of maps, such as thematic maps portraying nominal categories, or quantitative maps that use proprtional symbols or shaded areas (choropleths) to portray summary statistics.