The map of aftershocks from the Chilean earthquake last week reveals the incredible number of strong quakes that continue to jolt the region. Unfortunately, maps produced by the USGS and picked up by USA Today are inappropriately thematicized. The map shows the location of aftershocks marked by large circular symbols that are color-coded according to their most recent occurrence. Those that have been felt within the last hour are red; within the last day are orange; and those within the last week are yellow. It is a totally confusing way to map mainly because the idea should be to recognize both the location and severity. As they are portrayed, the symbols are all the same size and completely obscure most of the information.
Here's my suggestion: Keep the color-coding but use a graduated symbol to represent the aftershock's magnitude. this would help cut down on what is now a very cluttered map. And it would have been a nice addition if it showed the major fault lines as well.