Receiver errors from software or hardware failures can cause errors of any size. This factor should be taken into account when comparing GPS readings to a topographic map. A DRG is a scanned image of a USGS topographic map. The image is georeferenced to the Earth in the UTM coordinate system, which makes it ideal for use with GPS receivers. You can find information on GPS resources by doing keyword searches using one of the many Internet search engines available.
Site contains access to survey monument control data sheets and coordinate conversion software.
U.S. Coast Guard Navigation Center - Site contains GPS satellite almanac and orbit information. This document has undergone official review and approval for publications established by the National Mapping Division, U.S. Geological Survey. Some figures, have been modified or added to improve the scientific visualization of information.