Layer Name                 Type of Layer

Zip Codes                      Region
Counties                        Region
Interstates                     Line
Hospitals                       Point

Two of the layers have themes associated with them:

Zip codes have been color coded on the basis of the number of Myocardial Infarctions per square mile which occurred during 1995. Red zip codes had at least 36.9 per square mile while the lowest category (blue) had under 6.2 per square mile.

Hospitals have been sized based on the total number of beds at the hospital. Hospitals assigned the largest triangle size have at least 1,934 beds while hospitals which are the next largest size have at least 1,291 beds, etc.

Note that:

Each layer which has a theme also has a theme legend to indicate how it should be interpreted.

There is a Layer Legend which indicates how each layer is displayed so that each layer can be readily identified on the map