Map Symbols & Legends

The symbols and legend included on a finished map are details carefully chosen by the map's designer- they convey the primary meaning of the map, and, if they are unclear in any manner, can arguably obscure the map's intended purpose.  In the case of symbols rendered proportional to the relative size or magnitude of the thematic feature, it is imperative to choose colors and shapes that maximize the viewer's understanding of the phenomena being displayed on the map.

The above thematic map intends to convey the net increase and decrease in jobs for each state in the U.S. for the period between 2007 and 2015.  The circle sizes are proportionate to the magnitude of net loss/gain, and the color indicates whether the number of jobs represents an increase or decrease.  The legend, in the lower left corner, uses hollow circles to represent the relative numbers, as it applies to both the increase and decrease amounts, and indicates the colors red and green represent the net loss and gain.  The increase and decrease amount circles on the map are two feature classes, created by querying and exporting both sets of values from an original layer that contained both positive and negative values in its attribute table.  This was accomplished by adding a field to the feature class containing negative values, and calculating the absolute values of those numbers, as the layer symbology, as a display of proportional symbols, does not support the use of negative values.  Thus, each layer- one representing net increase, and the other net decrease- is symbolized separately, but with the same symbol range, which allows each set of values, both negative and positive, to be symbolized in differently colored circles.