UTM-USNG coordinate system for emergency responders

Which Coordinates Format for Reporting Location to SAR Emergency Responders

Geographical coordinates formats can be converted from one georeferencing system to another. But I wondered which format might be preferred by SAR (Search And Rescue) operators and/or emergency responders.

In my opinion, any hiker/backpacking/wilderness-traveler, etc.. with a smart phone should have a GPS app, and know how to get their location coordinates.

The other day I had a need to accurately identify True North. I own several descent compasses, and I know the magnetic declination where I live. I knew that I could get pretty close to True North with sighting my compass – which is what I did. However immediately afterwards, my inner tech-geek begged me to play with my iPhone compass and navigation apps. To see how good a job (or not) that I did with the compass.

Given my occasional propensity to get things ‘perfect’, I could see on the app that my established True North position was just slightly off, so I re-tweaked the project. While using the compass app, and also seeing the additional information displayed with my present location coordinates, it reminded me of a curiosity I’ve had…

Is there a particular coordinate system most often used by SAR / emergency responders, SAR operations, forest service, etc..?

Do they prefer to use one coordinate format system over another? If yes, then which one? I would select that one on my app as the default for ‘just in case’.

If one were to become in need of rescue (there are many hypothetical scenarios), a phone app could be used to determine one’s location coordinates that you could relay to search-and-rescue on a call. And again, although they could convert to whatever it is that they use, why not set it to that format to begin with…

Well I found the answer in the “Land Search and Rescue Addendum” to the “National Search and Rescue Supplement” to the “International Aeronautical and Maritime Search and Rescue Manual”, downloaded from the Homeland Security Digital Library.

The answer begins on page 4-44 (source PDF) and is spelled out in the table on page 4-51. Additional online searching reveals the same answer…

Primary Georeferencing System for Land-based SAR / Emergency Responders

At least in the United States, Land-based SAR responders (apparently) use the UTM numerical grid (Universal Transverse Mercator) map projection system along with the U.S. National Grid standard/format, USNG.

It is a grid-based method of specifying locations on the surface of the Earth. Think of it as a huge grid of 1 meter squares laid over a map of the earth.

(Learn more about UTM)

Secondary Georeferencing Coordinate System

The secondary coordinate system for emergency responders is Latitude/Longitude DD-MM.mm (Degrees, Decimal Minutes). Note this is the primary georeference system for Aeronautical SAR responders.

Note there are three ways to state latitude/longitude.

  • DD.d (Decimal degree)
  • DD-MM-SS (Degrees Minutes Seconds)
  • DD-MM.mm (Degrees Minutes)

Which format to use while reporting your coordinates to emergency responders?

First of all, use whatever you have! Dispatch or coordinators will figure it out to relay your location to SAR responders in their preferred format. Search teams will likely be using topo maps. They may convert the coordinates to their preferred format, if it differs. There are lots of agencies out there. Just because apparently many of them may use UTM, it doesn’t mean that another may prefer and use latitude/longitude in degrees and decimal minutes… (or any of the three ways to state lat/long.)

While researching this, I read the following comment from a forum discussing this very issue:

“I would recommend UTM coordinates; it avoids the formatting uncertainty of lat/long and is better suited for ground operations. (Easy to translate to paper maps, define search areas, and calculate distances.) If you use the WGS84 datum, the numerical portions are also identical with the military grid reference system (MGRS) and the national grid (USNG).”

If you who are reading this are involved with SAR and/or you are a emergency responder, let us know what your agency uses in the comments below.

GPS App on your phone

Most everyone these days has either an iPhone or Android phone. There are many various apps which include readouts of your coordinates. GPS apps. Compass apps. Navigation apps. And those apps vary with regard to which georeferencing/coordinate system they display.

Some apps have more choices for this in the settings/options. I suggest that either UTM or DD-MM.mm (Latitude/Longitude) would be good choices for a default. I have found that most all related apps will display latitude/longitude (in a variety of several possible formats). The more well known apps include the UTM format too. I’ll let you know what I’m currently using in a minute…

TIP: If you are ever in the situation where you need to report your coordinates to emergency responders, ask the person on the other end to repeat back what you’ve just told them! Getting a digit wrong may wind up far away from your actual location (depending on the digit)!

Examples of UTM coordinates versus DD-MM.mm

It’s beyond the scope of this article to explain how to use UTM or latitude/longitude. There are lots of online resources if you’re interested. With that said, I simply want to show you an example of each.

Lets find a location to reference. Lets use the Washington Monument. This is how the coordinates would be displayed for UTM, and lat/long in the DD-MM.mm format:

18S 323479 4306481

38° 53.36904N 77° 2.11674W

My default iPhone compass app displays lat/long. in DD-MM-SS (the format cannot be changed). The neat thing is you can press and hold on that readout, and copy it so you can paste into a text or email, etc..

I also downloaded “Commander Compass”. The free version has lots of cool features, including the ability to switch coordinate formats (including UTM).

I’ve had the Gaia GPS app for some time. It can also display UTM and other formats.

Years ago I purchased a handheld Garmin GPSMAP 64st. It has many built-in options as to how to display your coordinates, including UTM, USNG, etc.. I would use it while out in the backcountry, trails, snowmobiling, etc..

There are lots of related apps! For those who happen across this post, I’m curious about which apps you prefer for this type of thing…

Handheld GPS units

[ Read: Map Basics: How to read Latitude and Longitude ]