## Plotting UTM Coordinates

 Excerpt from "The Complete Guide to Adventure Racing" A critical part of adventure race navigation is plotting CP's on your map by using UTM coordinates supplied in the race passport. Knowing how to use UTM coordinates to plot points can be a precise way to ensure that you mark the CP correctly on your map.

In 1947, the U.S. Army adopted the Universal Transverse Mercator (UTM) projection and grid system. Using this system makes finding map coordinates easier than relying on lines of latitude and longitude. It is currently used to determine checkpoints (CP's) in many adventure races across the world.

The UTM structure creates 60 zones upon which to the earth is divided. Each zone is 6 degrees wide in longitude and 8 degrees of latitude. The zones span from the latitude 80 degrees South to 84 degrees North and are identified in numerical order starting with 1, which is on the International Date Line (180 degrees longitude) and proceeds east. The Polar Regions use the Universal Polar Stereographic (UPS) grid system.

Each zone is also assigned a letter from "C" to "X" with the exception of "I" and "O" to avoid confusion with "1" and "0" respectively. When reading UTM grid coordinates, we first examine "easting" which is the distance (in meters) eastward and then the distance north which is referred to as "northing." When looking at a map, you read right then up, or "in the door, then up the stairs." At the pre-race briefing, if the race organizer uses UTM grid points, your checkpoints will be located where the easting and northing coordinates intersect.

It is important to understand this system to properly plot your checkpoints on your race map. You will be given a series of numbers. Because we focus on small, specific areas when navigating the land, we will typically work with abbreviated values.

If you are given six digit numbers, that means you are covering a span of 100 square meters. Eight digits magnify an area to within ten square meters. All USGS topo maps that have been printed in the last three decades have blue "UTM grid tick marks" in the map's margin. When determining your exact location, each square is then further divided into one hundred boxes, which are created from ten tick marks going both east and north.

To determine the map location of a CP from a UTM grid value, go through the following steps:

1. Using the UTM value "864 558" look at the bottom of your map to find the east of the UTM grid line. In this case, "86".
2. Look at the margin on the right side of the map to find the northing of the UTM grid point. In this case, "55".
3. Divide the zone revealed by the easting and northing points into 100 boxed by marking ten equal ticks on the southern line and ten ticks on the western line, or use a transparent UTM plotter tool overlay that already has the tick marks printed on it.
4. Count the ticks from left to right to equal our next easting digit. In this case, "4".
5. Count the ticks going upward to equal our next northing digit. In this case, "8".
6. Our UTM point is located at the point where our easting and northing ticks intersect.

At first plotting UTM coordinates may seem complex, but after a little bit of practice with a real topo map then plotting points will become second nature.

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