Maps: Finding and Understanding UTM Coordinates
The NatureMapping Program is interested in knowing where wildlife is found. All wildlife use certain habitats for their needs. NatureMapping is interested in habitats that are the size of football fields (approximately a 100 meter x 100 meter area) or larger.
It is important that you know exactly where you observe different species. For each football field-sized (1-hectare) or larger area where you observe wildlife, you need to know exactly where that area is. Iowa NatureMapping requires that you use the Universal Transverse Mercator (UTM) system, a way of pinpointing a location with a set of coordinates, to locate your study area(s).
How to Use the UTM System
  1. UTM stands for Universal Transverse Mercator. It is one way to pinpoint a location on a map. UTMs are coordinates. Coordinates are a set of two numbers.
  2. UTM numbers are measured in kilometers, which can be converted to meters and vise versa. Example 1: 400 kilometers is equal in distance to 400,000 meters. Example 2: 200,000 meters is equal in distance to 200 kilometers.
  3. UTM numbers coincide with a light blue tick mark along the edges of the 7.5' U.S.G.S. quadrangle maps. Some 7.5' quadrangles don't have the blue ticks, but instead have a fine black UTM grid laid out over the entire map (similar to the grid shown in the graphic on the last page).
  4. Why do UTM numbers look funny? UTMs are numbers that are printed in black along the left, right, top, and bottom of the 7.5' quadrangle map. The individual digits of each number are printed in two different sizes. This DOES NOT indicate where a comma or decimal goes. Apparently, the different sized digits help the reader distinguish UTM numbers from the myriad of other numbers printed along the sides. Some of the other numbers along the sides of the map represent latitude and longitude coordinates and township and range numbers.
  5. The UTM system is laid out in a grid pattern. Think of finding a UTM coordinate like finding an (x) and (y) point in Algebra. In Algebra, it is called the Cartesian coordinate system.
  6. There are two numbers in a UTM coordinate. The first number coincides with an east direction (or "Easting"). This is (x). These numbers can be found along the top and bottom of the quadrangle. The second number coincides with a north direction (or "Northing"). This is (y). These numbers can be found along the left and right sides of the quadrangle.
  7. 1 kilometer = 1000 meters. Each UTM grid square is one kilometer, or 1000 meters, on each side. Each UTM number marks off one kilometer at each grid tic mark or grid line.UTM Coordinates continued...
  8. Always "read RIGHT, UP. Read to the right (like you read a book), and then read from the bottom to the top. In other words, find the distance to the EAST, then the distance to the NORTH.
  9. Once the kilometer numbers are found, you must narrow your coordinate to a set of numbers to the nearest meter. UTM coordinates can be found accurately to the nearest 25 meters using a 7.5' quadrangle map and an appropriate scale bar. For NatureMapping, find the UTM coordinates to the nearest 100 meters.
  10. Each set of UTM coordinates correspond to a given Zone. Most of Iowa is in Zone 15. Part of the state is in Zone 14, which includes parts of Lyon, Sioux, Plymouth, Woodbury, Monona, Harrison, and Pottawattamie Counties in western Iowa. See the zone diagram located in this handbook.
  11. To find out which zone you are in, look in the lower left corner of a 7.5' quadrangle map.
  12. An example of a UTM coordinate: UTM coordinates are written 454,250m E. x 4,661,500m N., Zone 15. (Read: four hundred fifty-four thousand two-hundred fifty meters east by four million six-hundred sixty-one thousand five hundred meters north, Zone fifteen). Always include the zone in your UTM reading. The UTM numbers are exclusive to just one spot in each zone, however, the same set of coordinates are used over again in every other zone. Look at the diagram at the end of this section to see how this UTM coordinate was found.
  13. Why not use latitude and longitude or the tier, range, and section (TRS - often called township, section, and range) to describe a location? The advantage of using UTMs is that they are precise points based entirely on actual distance. On a map, distance and area are important. When you lay out your monitoring site for NatureMapping, you can use the UTM grid scale on a 7.5' quadrangle to measure the area. Latitude and longitude (or Lat/Long) coordinates are precise points as well, yet the information is not distance-based. You've probably noticed how the longitude lines (those running vertically on a globe) converge at the poles. This convergence makes it difficult to convert "degrees" traveled west to east into "distance" traveled west to east. In other words, a degree traveled West to East near the poles is not equal in distance to a degree traveled West to East at the Equator. Tier, Range, and Section does not describe a point like UTM coordinates. Rather, it describes an area. Although we want you to keep track of wildlife in given areas, coordinates are much easier to map out using the GIS software we use. Also, the method for writing TRS descriptions is lengthy and cumbersome when describing an area to any degree of accuracy. Of course, technology is constantly changing, and now there is a web-based TRS to UTM coordinate converter. You can find this converter at The UTM coordinate is found by entering a tier, range, and section for a given area. The computer sends back a UTM coordinate for the center of the area you described using TRS.
  14. Another advantage of using UTM coordinates is that they are increasingly becoming the convention in other monitoring programs. The UTM is also one of many coordinate systems included on hand GPS (Global Positioning Satellite) units. GPS units continue to gain popularity with the public and can be used by NatureMappers.
  15. One final detail: Datums. Maps are created using surveying methods that maintain their accuracy in relationship to the actual earth. The accuracy of UTM coordinates relies on these methods. The surveying data is referred to as a Datum. 7.5' quadrangles rely on a datum using 1927 surveying data. This datum is called North American Datum 1927, or NAD27. For each set of UTM coordinates you find, you must reference the datum. So, for UTM coordinates found on paper 7.5' U.S.G.S. quadrangles, you would include NAD27. Note: UTM coordinates found using the Iowa Geographic Image Map Server (web-based coordinate finder) use a 1983 datum (NAD83). GPS Units can be switched back and forth.
Additional Resources
Artist: Mark Müller