Consult the map legend for the units used.
Maps use a calibrated set of datum, sometimes referred to as units, to represent the approximate shape of the Earth. This datum is then transferred to the map in terms of scale and size. Reading your map requires you know the units used, especially if coordinating it with a GPS unit. Most backcountry maps are topographical maps made by the U.S. Geological Survey (USGS). To find the units used, consult the map legend and datum.
Instructions
1. Spread out the map on a flat surface. If it is a USGS topo map, look to the far left lower corner to find the small print.
2. Read the map datum, often represented first by a year the map was updated. For example, you may see something akin to "1927 North American Datum." Read all of the information following the datum indicator for the map units used.
3. Read the information and look for the units of datum. For example, it may read "10,000 foot grid based on California coordinate datum. Sector 2. 1000 Meter Universal Transverse Mercator grid ticks." This indicates the units used, in this case the California coordinate datum, Sector 2 at 1000 meter UTM.
4. Look for the unit indicators of most maps, aviation charts and nautical charts in the lower left hand corner.
Tags: units used, California coordinate, California coordinate datum, coordinate datum, coordinate datum Sector
