Different maps have different coordinate systems. The two most common systems, used by the US Geological Service TOPO maps, are:
- Latitude (LAT) and longitude (LONG), with units of degrees, minutes and seconds.
- The UTM (Universal Transverse Mercator) Grid system, with units of meters.
LAT/LONG is system of units most of us are familiar with. The distance of a location from the equator to the poles is identified by latitude 0 to 90 degrees north or south (horizontal lines on the globe). Going around the earth east or west, the earth is divided into 360 degrees (vertical lines on the globe). The line that passes thru Greenwich, England is called the prime meridian, and longitudes are measured to 180 degrees east and west of this line. It is difficult to manually measure distance between two points using this system because the size of a degree varies with ones position on the round earth.
The UTM system
The UTM system is one that is preferred by map users who need precise distance information. This system selects a meridian and identifies how far east or west of that meridian you are and how far north or south of the equator you are (in meters). If you are unfamiliar with this system, but have a UTM map or need the accuracy that this system provides, please look into it further.
Most GPS units allow you to choose LAT/LONG or UTM, or other systems, as your coordinate system when you use the setup mode. When you have the coordinates of your position, you can look it up on a map and know just about where you are (depending on the accuracy of your unit). When you look up your destination on a map, you can input these coordinates and save the position in your GPS unit for route planning. Transparent plastic rulers to use with TOPO or UTM maps are available to make it easier to estimate a coordinate from a map. Some GPS units have a feature that allow you to identify coordinates of a position on a map by just using the map name, and scale, and by measuring how many inches the position is from the lower right hand corner.
Of course, the products to enhance GPS receiver capabilities are becoming more available, and less expensive. Keep an eye out for new software products with exciting features, that seem to come out every month. There are Atlas-type software, with streets, highways, restaurants and hotels, that let you find almost any address in the continental US. There are topographic-type map programs for several regions with real USGS TOPO maps or hiking guides for popular mountainous areas (with more coming soon). There are new PC Cable+software bundles being offered by GPS manufacturers to upload/download GPS information. Some GPS units can be connected to a portable computer, with mapping software, and will actually track REAL-TIME, your location on the PC screen. GPS application will continue to evolve and improve like computers, but DON'T WAIT, if you need to use it NOW.