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Suppose I am out in the wilderness and an emergency arises. I have an accurate fix on my location (from GPS, map and compass, astronomical observation, etc...). I manage to get in touch with emergency services and need to tell them where I am.

But there are many different formats I could use to report my position.

  • Latitude and longitude in degrees / minutes / seconds

  • Latitude and longitude in decimal degrees

  • Latitude and longitude in degrees and decimal minutes

  • UTM

(And with any of these systems there is the finer question of which Earth ellipsoid or datum my map or GPS is based on, which could make a difference of a few tens or hundreds of meters in the position; in dense forest this could make it considerably harder for rescuers to find me.)

Obviously I want to avoid any confusion; if I give my position in (say) degrees / minutes / seconds, and a helicopter pilot blindly types it in their GPS which is set to decimal degrees, they'll go to the wrong place (perhaps many kilometers away). UTM is less ambiguous, but will they even know what that is? I may be speaking to a dispatcher in an urban office, perhaps over a noisy and unreliable phone or radio connection, and that's hardly the time for a technical discussion of the fine points of geodesy.

So in short:

  • Is there a particular position format that's preferred by emergency responders?

  • Are dispatchers and responders sufficiently trained to understand the difference between these positions, so that I can use any format if I tell them which one it is?

  • Are there other general "best practices" for this situation?

I suppose the answers may differ between different countries or regions (I'm in the US) or between land and sea emergencies (I'm usually on land).

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  • 1
    Datum differences are not large enough to cause a problem. And seconds is usually more accuracy than needed. It is standard to use DD MM.M for most navigators.
    – user6972
    Jul 6 '14 at 8:14
  • UTM over DTMF. A ES operator is not likely to have means to or knowledge to decode whatever protocol you choose. DTMF on the other hand is designed for bad connections from the end of the Long Lines era and is simple enough.
    – Justin
    Aug 17 at 10:41
  • "Send a DSC position request to my VHF" or "Should I activate my PLB?" might be the most useful ways to transfer position data to rescuers. Aug 23 at 16:09
15

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). In my area the local mountain rescue groups (BAMRU, Tahoe Nordic) use UTM.

That said, aircraft and ships at sea usually prefer latitude and longitude values as the numbers don't "reset" when you cross zones, and they are usually covering much greater distances than people on land. Per the addendum I added at the end, the recommended format is degrees and decimal minutes. The linked PDF suggests reading coordinates as in the following example (for 39° 36.06’N by 76° 51.42’W): “Three nine degrees, three six decimal zero six minutes North by seven six degrees, five one decimal four two minutes West.”

Regardless of coordinate system, have the person on the other end repeat the numbers back to you; this is one set of numbers you don't want to have an error. Writing down your message before communicating will also help you with a poor connection or low batteries as you'll avoiding wasting time trying to remember what else you need to communicate.

Finally, as others mentioned, the dispatcher should be able to handle any coordinate format, and any search teams will be using topo maps and translating the coordinates to their preferred format. (They are usually familiar with the areas they regularly work in.)

Addendum: I suspected that [within the US] UTM was becoming a SAR standard, as a quick Google suggests that to be the case. Further digging indicates the National Search and Rescue Committee has designated the US National Grid (USNG) system as the standard coordinate system for land-based SAR in the United States, and latitude and longitude (in decimal minutes) for aircraft and boats. This does not mean that some (many?) local agencies are no longer using their older preferred systems; full compliance is probably many years away. If you want to know more about USNG, I suggest posting a separate question, but here's a comparison:

  • USNG: 18S UJ 23371 06519

  • MGRS: 18SUJ2337106519

  • UTM: 18 323371 4306519

(Note that USNG and MGRS use a letter pair for the 100km grid squares whereas UTM doesn't; UTM instead has additional digits. The Easting and Northing values always have the same precision: 3x3, 4x4, and so forth. I personally prefer the USNG style.)

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I'd give them whatever my device or map provided me, and let them convert to whatever their devices or maps use. Anyone used to receiving lat/lon coordinates regularly should be able to convert from various formats to whatever they use internally.

You're the one in trouble with limited resources. You're out there with a broken leg, lost, in the cold or dark, or whatever. You're a lot more likely to screw up than someone sitting in a office who is professionally used to dealing with this and probably has equipment that does conversions for him routinely.

You are over-thinking this.

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  • Of course you are right - when in an emergency situation you shouldn't overthink it. However, I like to view this question as, if I were to prepare a trip, and for each of the formats I have exactly one device. I can only bring one with me, which one should it be?
    – nhaarman
    Jul 5 '14 at 9:32
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    @Niek: Bring whichever device is most suitable for your outing. What format it displays location in wouldn't even be on my list. In the unlikely event that you need to communiate those coordinates to rescuers, they'll deal with whatever you have. Otherwise, you want the most convenient device for your purposes. Jul 6 '14 at 13:29
  • 1
    I would add: including the units, coordinate systems your device/maps provides. Do not just give numbers.
    – user15958
    Sep 11 '18 at 14:39
  • @Jan: I agree, although any competent first SAR person you talk to is going to ask what the units are if you just give him a bunch of numbers. Sep 11 '18 at 16:13
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Always have a water proof map of the area you're traveling in ( one with coordinates on each side if you can help it ), and a compass you can use to triangulate your position with. You'll be better prepared in an emergency and more confident outdoors in general if you practice triangulating your position until it comes naturally: http://www.rei.com/learn/expert-advice/navigation-basics.html

As a backup, have a reliable GPS, and carry extra ( fresh ) batteries for it, more than you think you will ever need. Obviously having your coordinates in an instant will save you time, but electronics aren't to be trusted with your life.

If you can give your coordinates to dispatchers, you're leaps and bounds ahead of most people that need assistance ( have the dispatcher confirm your coordinates ). Most search and rescue teams have the skill and equipment to translate your coordinates into their preferred format faster than you can even read them.

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    My preferred hiking area is forested--I would consider GPS more reliable than map & compass. Sure, something can happen to your GPS but if I was in a position to need to summon search & rescue I very well might not be in a position to get enough visibility to figure out where I was with the map. Sep 12 '18 at 2:51
  • 1
    And I'll add that if it's after dark the chances of figuring out where I was from my map would be zero. Even with a nearly full moon the only terrain I could see was the contours of the horizon near the moon. Even if I could have matched that up with my map (not likely as it was actually multiple pieces of terrain) it would only give one bearing. Aug 22 at 0:32
  • @LorenPechtel if you can see your GPS you can see your map, and if you can't read a map you don't have much business being out in the wilderness to begin with. Aug 22 at 5:10
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    I'm not talking about seeing the map, I'm talking about seeing the actual features to compare to the map. The only terrain feature that could be discerned was the ridgeline the moon was rising over--and I know that it's really two separate features. (And I was only seeing that much because I was in an area that burned 8 years ago. Once I was past that and back in the forest there were zero landmarks.) Aug 23 at 1:52
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In the marine environment, it's often a little easier if you reference a known location. Offshore, you want to use lat/lon coordinates for sure.

But if you're a mile from the coast (or less), it's a lot easier for people to find you if you say "We're a hundred yards south of buoy three, looking at the hotel with the red roof."

I worked for a water rescue service for a bit, and it takes time and clarity to hear a full string of coordinates across a VHF connection. Also, if you're a single minute of latitude or longitude off, that's a big difference. Plus, those same coordinates need to be manually plugged into a chartplotter, which takes time and can't be done while the boat is racing towards you.

But the people who are coming to get you inshore on the water are very familiar with the coastline and will know buoy #3 instantly, and there's no way you're going to know the red roofed hotel unless you're really staring at it.

So while not to discount coordinates, stating what you can see around you is a great confirmation and at least where I worked would get me headed in your direction ~30 seconds faster and with a bit more certainty.

4

If you're in Britain, you can either provide GPS coordinates in latitude and longitude as normal, or an Ordnance Survey grid reference which is easily obtained from the maps normally used in Britain, or using the OS Locate app on a GPS-equipped smartphone. The OS grid is essentially a transverse-Mercator projection, but is not the same as UTM.

Probably mountain-rescue teams would prefer OS grid coordinates, because they will refer to OS maps for their own navigation. However, I expect they also have GPS units which can perform the conversion automatically.

An OS grid reference formally consists of two letters, identifying a general regional grid, followed by six digits (three for eastings, then three for northings) which identify a location within that grid to within 100m. The grid squares marked on OS maps intended for hiking (eg. Landranger series) are normally 1km square; road maps often have 10km squares instead.

There should be a legend on each map explaining how to construct a full grid reference from the map, as well as the local relationship between "grid north" and the magnetic and true norths.

3

Probably the most important things are to use the data it's easiest for you to get, and to state clearly what system you are using. If your phone or GPS gives you decimal lat/long, give the rescue services that. If it gives you DMS or UTM, give them that. Rescue services will be better at converting than you, the stressed, injured and frightened victim. If you explicitly say:

fifty one decimal five zero one latitude, negative zero decimal one four four zero longitude

or

fifty one degrees thirty minutes five seconds north, zero degrees eight minutes thirty nine seconds west

then you are unlikely to be mistaken. A rescue service is going to be able to convert as long as they are sure what you are using.

For completeness some emergency services are using what3words to locate incidents. Although it's under scrutiny for having some similar sounding nearby places it's easy for the victim to get right even if they are stressed, injured and frightened.

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  • How do you get a what3words position from a map? Sep 4 at 11:11
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I have twice had problems with this in working with groups in emergencies. The group mistakenly reading decimal minutes as DMS, adding in unnecessary delays in reaching the group. In conversations with lifeflight personnel they say they can use any format, but prefer DMS. All the groups that I work with on policies I insist on them using DMS for that reason.

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I'd give my position in terms of landmarks ("I'm about five miles up Independence Creek; look for the silver emergency blanket draped over the bushes"). If I had a GPS, I'd also give coordinates in whatever units it displays. If you've ever gone geocaching, you'll know that while coordinates are precise, they don't tell you what the terrain is like or which direction to approach from; landmarks can.

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    Land marks are only good if they know what area you are in to start with. Also local names often differ from map names. And different maps might use different names or have multiple landmarks with the same name. In many parts of the world land mark names are too undefined to be universally recognized by rescue teams. This is especially true along shorelines.
    – user6972
    Jul 6 '14 at 8:17
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    It's not like your SAR team is in a call centre on the other side of the world. They are in the area and they know the area, too. "I'm on a ridge north of Jack Lake" and then some co-ordinates - this sanity checks the co-ordinates also. Jul 15 '14 at 19:01
  • @Kate I've heard stories of people calling emergency services using mobile phones and being connected to quite distant call centres, with operators who clearly do not know the territory. (So use a real phone unless mobile is the only choice.) In any case, callers don't normally talk directly to SAR members, so the message is likely to be written/typed and then passed to the team, so make sure that it's absolutely clear and unambiguous. Aug 23 at 13:47
  • @TobySpeight I guess everyone's mileage may vary but the one time I called the coast guard they were able to figure out where we were from "it's a bay and the road comes really near" kind of thing. This was pre-GPS being so popular. Aug 23 at 14:40
  • @Kate that might have worked so well because you called your coastguard directly, rather than the general (112) emergency number. I still think it's good to consider that your message might get written down and passed from one person to another. Aug 23 at 16:07

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