Spatial Thinking in Planning Practice: An Introduction to GIS

30 ` Figure 4.4. A “proportional circle” map that depicts count data. Source: G. Hatchard. https://www.e-education. psu.edu/geog482fall2/c3_p17.html MAPPING RATES AND DENSITIES A rate is a proportion between two counts, such as Hispanic population as a percentage of total population. One way to display the proportional relationship between two counts is with what ArcMap calls its Pie Chart option. Like the Proportional Symbol map, the Pie Chart map plots a single symbol at the centroid of each geographic area by default, though users can opt to place pie symbols such that they won’t overlap each other ("is option can result in symbols being placed far away from the centroid of a geographic area.) Each pie symbol varies in size in proportion to the data value it represents. In addition, however, the Pie Chart symbol is divided into piec- es that represent proportions of a whole (Figure 4.5). Figure 4.5. A “pie chart” map that depicts rate data. Source: G. Hatchard. https://www.e-education.psu.edu/ geog482fall2/c3_p16.html Chapter 4: Mapping People with Census Data