What: Typically on reference maps, atlases, and locator maps, point symbols for cities and towns are based on population and political function. Larger cities have more prominent symbols and labels. On this map the cities are symbolized using three different point symbols that relate to the size of the city's population. Why: Using variation in point symbols for cities on maps provides visual hierarchy that allows readers to distinguish different classes of features. It is important to show villages, towns, small cities, large cities, and capitol cities distinctly to avoid readers drawing incorrect conclusions about the relative importance of the places shown. For more about using point symbols to show different kinds of places see pages 144-149 of Designing Better Maps.
As a rule this works when making a locator map in a given region such as the one above. However, when the map shows an extent where there are densely populated regions and sparsely populated regions, it will be necessary to incorporate more information, such as notoriety or local density of places, to decide which places should be shown in the sparsely or densely populated regions.
How: To symbolize the cities we classified them into three classes by population and applied different symbols to each class. We chose three classes because this was a simple locator map, because we did not want a more complicated portrayal of the cities. Our goal was to show where they are and relatively how important they are. We stored the class assignments in the attribute table so we could use them to make similar maps in the future. Here are the steps we followed:
We symbolized the city classes as follows:
We also used our PopCat field values as the basis for label placement which is further described in Labeling cities along coasts.
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