How to Overlay a UTM Grid
The Universal Transverse Mercator (UTM) grid system is a Cartesian-coordinate global mapping system used in lieu of coordinates expressed in longitude and latitude. An overlay is a tool to place along grid lines and read the coordinate quickly. Made of clear plastic, the overlay allows the map reader to simultaneously see the map surface and the numbered lines on the overlay. The numbers on the line of the map are combined with numbers read off the overlay to communicate a point location. Invented by the US Army along with the UTM system, the overlay allows precise position readings with moderate effort for the map-reader.
Things You'll Need
- Universal Transverse Mercator topogrpahical map
- Pencil
- Clear platstic UTM overlay, scale appropriate
Instructions
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1
Get the overlay that is sized correctly for your UTM topographical map. It is expressed in a ratio: one inch of map distance to X inches of map distance. Example: 1:50,000 is a standard military UTM map and means 1 inch of map distance equates to 50,000 inches of ground distance. An overlay is used to identify a numerically-expressed point on a UTM map.
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2
Look at your map. Individual grid squares represent one square kilometer of ground surface. The Overlay has a north-south line that corresponds to the north-south axis in a grid square; and an east-west line that corresponds to the east-west axis of the grid square.
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3
Align the north-south line(s) with the N-S side(s) of the grid square; and align the east-west line with the "bottom" or southernmost line of the square. Each line is graduated into 10 equal segments. The ground distance represented between each graduation is 100 meters.
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Read the map's grid lines. Each north-south grid line in UTM is represented by two numbers. Each east-west grid line is represented by two numbers. Once you know what grid square contains the position in question, the number of the left N-S line is your index, and the E-W line on bottom is your index. That square is represented as the N-S number then the E-W number. For example, the left line reads 45; the bottom line reads 16. You are looking at the 4516 grid square, an area 1,000 meters square.
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Identify the point on the map and use the overlay to read, to the nearest 100 meters, where the target point is in relation to your grid lines. The point is somewhere in the grid square. It is X meters to the east of the left boundary of the grid square. It is X meters north of the bottom line in the grid square. Each 100 meters is expressed as a single digit, e.g., 200 meters east of the left-line is 2; 500 meters north of the bottom-line is 5.
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Your coordinate is properly expressed as a six-digit coordinate 452165: 45 + (2)00 m / 16 + (5)00m: 45-2 ... 16-5: 452165. This shows your position within 100 meters. You can communicate that coordinate to anyone with the same UTM map, and she will know where you mean.
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References
Resources
- Photo Credit map of the world image by Cristina Cazan from Fotolia.com
