The UTM Coordinate System

What is the UTM coordinate system and why should you care? We’ve made a video about it or you can read below if moving pictures aren’t your thing.

When you are exploring, whether on a trail or in the middle of nowhere it’s important to be able to figure out exactly where you are. This is where the UTM coordinate system can help.

What is UTM? UTM stands for Universal Transverse Mercator. I’m going to cut out a lot of detail and just say the UTM system divides the world into a series of squares. This makes a lot of navigation problems easier like where am I and how far am I from camp. Since the earth isn’t a cube the maps have some distortion. However most people who use UTM are in such a small geographic area that these distortions are minor.

How does it work? UTM coordinates have 3 sets of numbers. The first set is the zone identifier which consists of two numbers and a letter. This one may not be on your 1/24,000 scale map. The second set is the East/West location called the Easting and the third set is the North/South location called the Northing. The zone identifier and the first two numbers of the Easting and Northing are often dropped.

What does it look like on our 1/24,000 map? Very few maps come printed with UTM grid lines but you can find the UTM grid marked by blue tick marks evenly spaced along the edges. The numbers will get bigger from South to North and from West to East. The numbers enlarged on the maps edge represent 1,000 meter intervals. [1 mile = 1,609 meters]

How do you use UTM to find a location? Find the location that you are interested in. I’ll use a radio tower which is located East of the 61 Easting but not the 62 Easting and North of the 65 Northing but not the 66 Northing. We would write this as 13T 0461000mE 4565000mN or shortened to 61 65. But this is not very accurate, these coordinates would have an error estimate of 500 meters.

To get more precise you can break the 1,000 meter square into smaller squares each 100 x 100 meters. First you will need to draw the 1,000 meter grid lines on the map. You’ll also want some tools like a UTM square or you can use paper and the scale at the bottom of the map.

Then use the same technique to find the coordinates.  Identify the the closest Easting to the left of the location and the closest Northing below the location.  For the radio tower above you would get 13T 0461100mE 4565100mN.

You can then break down the 100 meter squares into 10 x 10 meter squares.  Then we could get a grid for the radio tower of 13T 0461130mE 4565190mN, which we would shorten to 6113mE 6519mN.  These coordinates have an error estimate of 5 meters (about 16 feet).

If you have any questions or want anything clarified be sure to ask in the comments or send an email to al@justtrails.com.  Also check out the first blog post in the Navigation Skills series: Introduction to Maps.

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