From ArcUser comes this excellent article about using “ring maps” to improve comprehension when mapping multiple variables.
“Document files, tables, and charts can summarize complex data, but they can be hard to read and interpret. However, a GIS-based map known as a ring map can help overcome this problem for location-specific data. A ring map is a map surrounded by a set of concentric, segmented rings that can be circular or elliptical in shape. Each ring displays an additional dimension (e.g., temporal) of data that represents an attribute of a particular location. Thus, the ring map shows more than geographic positions; it creates infographics that can organize and display several types of data organized using the simplicity and clarity of a map.”