Universal Transverse Mercator (UTM) is a coordinate system that describes a location on a map. GPS receivers can show positions via these coordinates; most maps, especially those for tourists, also use UTM coordinates. This type of coordinate is also widely used by search and rescue operators and is becoming more and more common in tour guides. In this article you will see how to interpret them.
Steps
Step 1. Determine which area you are in
The world is divided into 60 UTM zones
Step 2. Determine the datum to use
- To use UTM coordinates you need to make sure you are using a common UTM datum, or reference point - or "geodetic datum" - among the maps, GPS or other tools you use. For example, you need to make sure your GPS is set to the same datum as the map or travel guide, or you should make sure the search and rescue department uses the same datum as you for the coordinates you provided. These are just a few examples of the various combinations of navigation tools you may find yourself using.
- The most used datum points in North America are NAD27 CONUS and WGS 84.
- Here's how a geodetic datum works. The geodetic datum is a point on the map from which measurements are made for all other points. By choosing a different reference point, the coordinates can totally change. If you use two different datums on your GPS or map, you will end up in the wrong place.
Step 3. Determine easting
- The first number in the UTM coordinates is called “easting”.
- Easting indicates how far east you are.
- If you are using a map, look at the numbers along the edges, these correspond to the UTM coordinates. Easting coordinates are located on the top and bottom of the map.
- If you use a GPS, easting is the first number indicated in the coordinates in UTM mode.
- A change of 1 number in the easting coordinates, for example 510, 000 mE-510, 111 mE, indicates a ground shift of approximately 1 meter. If you walk from 510,000mE to 511,000mE without changing northing, you will have walked approximately 1km.
- Interpolate the easting coordinates on the grid to determine the exact point.
Step 4. Determine the northing
- The second number of the UTM coordinates is called “northing”.
- Northing indicates how far north you are.
- If you are using a map, look at the numbers along the sides that correspond to the UTM coordinates. The northing coordinates are on the left and right of the map.
- If you are using a GPS, northing is the second number indicated in the coordinates in UTM mode.
- A change of 1 number in the northing coordinates, for example 510, 000 mN-510, 111 mN, indicates a ground shift of approximately 1 meter. Walking from 850,000mN to 851,000mN without changing your easting, you will have walked about 1km.
- By interpolating the northing coordinates on a grid you will determine the exact point.
Advice
- The most common problem that can be encountered when using UTM coordinates are datums that do not match. If you are unable to use UTM coordinates, the first thing you should do is make sure that all maps, books and GPS systems you are using have the same UTM datum.
- To more accurately interpolate the coordinates, a scaled plastic grid can be used to superimpose the map. In any case, you have to make sure that the scale of the grid matches that of the map; if the scales do not match, the position on the map will be wrong.
