Universal Transverse Mercator (UTM) is a grid system that describes a person’s location in the backcountry. It is wonderfully simple to understand and use because:
- It is intuitive – it’s concepts can be understood quickly
- It can be easily self-taught
- Young hikers grasp this system easily
- A location on a map can be quickly determined.
- It is a selection option for Global Positioning System (GPS) receivers
Because of its simplicity, UTM is quickly becoming the principal grid system for hikers, hunters and Search and Rescue (SAR) teams nationally.
A navigation grid is a reference system developed by cartographers that can be used to plot a geographic position on a map. There are many grid systems available for use such as Latitude and Longitude and Universal Transverse Mercator (UTM). Many countries have their own national grid system. The UTM system is just like a Cartesian Grid. For example, the grid position below is just 2.2 units over and 2 units up.
Think of a grid as a series of defined squares on a map (see below.)
Cartographers have developed coordinates that are associated with the black grid lines. Together, these components define location on a map. The UTM grid lines form a series of equal squares on a map. On a USGS 7.5’ minute topo map (scale 1:24,000), the spacing between the grid lines is 1000 meters (1 kilometer.)
The coordinate values are known Easting’s (vertical lines) and Northing’s (horizontal lines.)
Notice how the Easting values increase moving from left to right and Northing’s increase from bottom to top. Coordinate values are always positive.
A key component to UTM grid is the identification of zone. The earth is divided into 60 zones. Every location will have a zone identifier. On the map above the zone is linked to the Easting value and is the first set of numbers. In this case the zone identifier is the number 10. GPS receivers display the zone value linked to the Easting, see below.
The letter “T” seen above is a secondary, horizontal (east-west) identifier. I personally pay little attention to it in my backcountry trips.
All USGS maps identify the zone in the title block at the bottom left of the map. Note that on some commercial maps the UTM zone identifier may not be in the title block and can be hard to find.
The UTM coordinate can now be refined to a meter. Again the spacing between the grid lines is 1000 meters (1 kilometer). On the maps above, the tick marks between grid lines are in increments of 100 meters. The hiker can then interpolate the distance between the tic marks. For example:
- A standard grid line coordinate might be 10 6 04 000. (The three zeros to the right are units of hundreds of meters.)
- A position 250 meters east of 10 6 04 000 would be expressed as 10 6 04 250.
The position of the large X on the map above would be described as:
10 5 25 270 East (the green line)
47 91 180 North (the red line)
The final three places will always be expressed (10 5 25 270 East.) The value 2 is in units of hundreds, the 7 is in units of 10 and the 0 is in units of 1’s. Thus, 50 meters would be written as 050. Otherwise, it could be considered as 500 meters instead of 50 meters.
Every point on a map (e.g., a mine, an intersection, a camp site, etc) can be described using UTM coordinates to the accuracy of one square meter.
I recommend consider carrying a small plastic ruler or other suitable straight edge when accuracy is important. For general hiking and backpacking, one can quickly estimate a current position in the backcountry without other map tools.
UTM coordinates of a destination taken from a map can be easily saved on a GPS receiver. For example, to do this the hiker “marks” a waypoint and then moves the backlit bar (yellow shaded area) from “save” to the “location” data field. The “location” data field is then edited per the receiver’s instruction manual.
A fine reference for more practical information about UTM grid is Lawrence Latham’s book GPS Made Easy. Chapter 5 has an easy to understand tutorial on this grid system; that’s how I learned it.
About Blake Miller
Blake Miller received significant hands-on navigational training during his 20 years of service in the US Navy. He has taught map and compass, GPS and wilderness survival classes in Central Oregon since 1998. As a part-time faculty member at Central Oregon Community College, he currently teaches land navigation classes to Natural Resource students. He has been an active member of the Deschutes County’s Search and Rescue (SAR) team since 2009. Blake is also a featured speaker at regional SAR conferences, Sportsman Shows, and Cabelas. His articles have been published in several national magazines. Blake can be contacted through www.outdoorquest.biz.