Maps are inherently very difficult objects to put in a web page.
Even so the graphic version of a map never has the detail or clarity of the printed map. Therefore most people who deal with electronic maps store and retrieve mapping data in the form of electronic databases. This page paints with very broad strokes and is intended to deal only with major sites, or sites dealing specifically with maps of geological interest. Some of the terminology may not be familiar so we have written a very, very simple introduction to the topic of databases and GIS information . United States Geological Survey .