What is a GPS?

Many maps, such as road maps, only deal with the two-dimensional location of an object without taking into account its elevation.  While convenient, these maps do not accurately represent the surface of the earth.   The earth is contorted ("relief"), and because of this latitude, longitude and elevation are necessary to locate areas exactly on a map (three-points, or "triangulation" is required to accurately locate something within 3-Dimensional space).  Maps that deal with three dimensions are called topographic maps. Topographic maps take into account the elevation of the area being mapped above a ‘reference datum’, thus showing the actual shape of the area.

Photographs, satellite imagery, surface and subsurface scientific exploration and other means of gathering data have changed the way modern maps are constructed. Recent computer technologies have allowed for the development of Geographic Information Systems which provide complex pictures of the earth - both on the surface and beneath it.  The global address of any place on earth includes both latitude and longitude. This coordinate system is widely used in all areas of navigation and related technologies. An example is Global Positioning System technology which uses a receiver to transmit a signal to satellites orbiting the earth. The GPS unit then uses the amount of time it takes for the satellite to receive its signal, and the satellite's position in the sky to calculate an exact latitude and longitude.

A GPS unit is the most accurate way to pinpoint your location. What is GPS? Developed by the U.S. Department of Defense to provide high accuracy positional information, Global Positioning Systems is now available to the public. Hand-held GPS units allow us to know our location and to deliver information to a GIS study for analysis. Data acquisition in the field is then faster, easier and eliminates errors. But lacking a GPS unit, it is possible to determine your location using a topographic map. While we prefer to receive the information in UTM's (Universal Transverse Mercator), latitude and longitude is also acceptable.

The USGS maintains an Internet utility similar to a GPS.  They can give you a set of latitude and longitude coordinates based on your geographic position. TRY IT!

Some Text Courtesy: Digital Atlas of Idaho