Maps ETC is a part of the Educational Technology Clearinghouse, produced by the Florida Center for Instructional Technology, College of Education, University of South Florida.

A friendly license allows teachers and students to use up to 25 maps in non-commercial school projects without further permission. All maps are available as GIF or JPEG files for screen display as well as in PDF for printing. Use the GIF or JPEG maps for classroom presentations and student websites. Use the PDF maps for displays, bulletin boards, and printed school reports.

Put simply these maps are available for educational use. The maps are grouped, and then presented in a chronological order, although there are some anomalies, it is rather time consuming to search through the maps, but the thumbnails help. This is certainly a service that can be made use of. I especially like the Google Earth Help page, which help one use these maps in Google Earth.