Proportional Circle

 I created this map using ArcGIS

This is a Proportional circle map showing the locations of earthquakes with a magnitude of 7 or higher on the Richter scale in California.  The large black circles represent the earthquakes and the yellow, smaller circles represent cities within a 20 mile radius of these events.  This map would be quite useful to analyze cities at risk of getting hit by a major earthquake and properly preparing for this type of disaster by changing building infrastructure and creating emergency plans. I uploaded the data and shapefiles from my GIS Tutorial Updated for ArcGIS 9.3.