Map legend

A map legend or key is a visual explanation of the symbols used on the map. It typically includes a sample of each symbol (point, line, or area), and a short description of what the symbol means. For example, a short segment of a blue sinuous line may be labeled 'rivers'. [1] Because map symbols’ meanings vary from region to region, a clear and concise legend is critical for conveying the distinctive characteristics of the map. [2]

The legend is a graphical representation of information, with design principles similar to a map or any other graphic. The only difference is that it is related to the information on the map it is connected to. Therefore, it is important to remember the layout design concepts such as harmony, visual balance, clarity, visual logic, logical groupings, and unambiguous references to create a legend that is effective in relation to the map. Creating a well laid out legend will enhance the overall gestalt of the maps visual appearance.

The legend should be simple and its position largely depends on the open space available in the map; a legend should be centered in an area of open space. It should be large enough that it is legible but small enough to stay low in the visual hierarchy.[3]

http://wiki.gis.com/wiki/index.php/Map_legend