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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: - 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".
- Look at
the margin on the right side of the map to find the northing of the UTM grid point.
In this case, "55".
- 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.
- Count the ticks from left to right
to equal our next easting digit. In this case, "4".
- Count
the ticks going upward to equal our next northing digit. In this case, "8".
-
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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