Long/Lat or UTM ??

Hey folks, I briefly looked for a thread on this but didnt see one.
I was wondering what the general feeling was on using either long/lat or UTM for back country navigation.

I am in charge of a search and rescue team, and we exclusively use UTM.

Since it's metric, you can estimate distances and stuff by simple arithmetics. 5210780 is 200 meters away from 512980. It's as simple as that.

UTM all the way!

I'm a novice geocacher and I like UTM for the same reason as SARbound.

Depends on what you want to do with it;'navigation' covers a lot of ground). GPS work? Pencil and paper with a map scale?

I make maps (on a topo base) so when I'm out mapping, ground truthing, whatever, using a scale that's base 10 is much more convenient - especially if it's raining, windy, really buggy, or you're otherwise distracted. I've always used UTMs.

This also holds true for coordinate transforms, like if you're using legacy data that's based off a different datum. Software tends to be more agreeable using UTMs...or at least it's easier for me to see where I screwed up.

I understand that most state agencies (Alaska's one; I don't know about others) use decimal degrees, so if you want to plot a mine shaft or, more importantly, call for an evacuation, having decimal degrees expedites the process. SAR and LEOs please chip in with your experiences! This would be a very good thing to know.

And, as a GIS wizard told me a few years back, UTM stands for "Use This Method."

The Search and Rescue folks all seem to like UTM and the pilots prefer Lat/Lon.

I like UTM because its a LOT simpler.

Our Medevac folks always asked for decimal lat/long.

One advantage of Lat/Long is that you can get it by sighting on the sun moon or stars as long as you have a watch with you.
If you are good at it you can get your location within about a mile. (1.6 kilometers)with pretty simple tools. Traditional navigators like it more.

That is not accurate enough for fine map work so when you are located on your map and doing survey work you usually use surface measurements. So miles or meters instead of degrees and seconds.
Surveyors like field measurements off grids more than angle measurements from stars.

With the UTM grid system and GPS units available you can locate on a mapped grid to within a few meters easily.
Modern GPS units can locate a surveyor to within 2.5 cm.
As Sarbound points out, with UTM you have an easy distance measurement that you don't really need to think about while with Longitude you have a reading you need to convert to ground measurements.
Universal Transverse Mercator does have a couple of other problems which Yelp's answer points out.
There are many different grids in use and they all vary on where their data points are. The data points (datum) is their model of the shape of the earth. It also involves the grid system they laid over it to measure from.
If you are using the wrong grid system it can throw you off.
The short of this is that you need your maps and GPS unit to be on the same datum. The datum will be noted on your maps.
They also need to be the same for the people you are communicating your locations with.
In North America the standard datum in use is North American Datum 83 which is also used for north America in the World Grid System 84.
However if you have an older map it might be NAD 27. Some USGS maps have grid marks for both. Military grids can be different too.
Usually the difference is only a few hundred meters between NAD 27 and NAD 83.

I think this was a good thread to start.

I use UTM for almost everything. It is easy to measure on a map with a scale card. Most of the time you don't even need the card and just estimating the grid is close enough.

Myself and Rantor went on a lil adventure today and were using lat/long and we were off by 1/2 mile. We eventually found what we were looking for, but half a mile off??? Next time - UTM!

Like many have said, UTM is much simpler to use and makes a whole bunch more sense for land navigation.

Also like others have said, pilots like lat/long. On most Garmin handhelds you can set one of the data fields in the trip computer to display Lat/Long even though you may have the GPS set to UTM. This allows me to look up my position in Lat/Long should aviation need it.

It is more complicated if given a Lat/Long coordinate I need to place on my map or in my GPS, but doable (set the GPS to the given coordinate system, enter the coordinates and set back to UTM). However, the biggest issue when two people are using two different coordinate systems is they are often on two separate map datums as well... there is at least one place in AZ where the difference between NAD27 and NAD83 is almost 800m... ask me how I know

My GPS uses whatever coordinates that are easiest to read on my paper map. In my country, that is UTM, and I think that would be true for the majority of maps in the majority of countries. I consider GPS a very nice addition to paper map and compass, but I take a "I love to use it as long as it works" attitude to the GPS and refuse to consider it my sole or primary means of navigation... Too much that can go wrong.


A nice twist to UTM is the MGRS system:
http://en.wikipedia.org/wiki/Military_grid_reference_system
The essence is that for an accuracy of 100 meters, you only have to deal with 3 decimals in each directions. Ordinary UTM coordinates are 10 decimals. I can remember two numbers of decimals, but not two 10-digit numbers, so it makes life a lot easier. On the maps I use, the kilometer markings are gridded and numbered, so I can read them directly off the page even when the map is folded. My GPS supports MGRS, but not everyone will.


And - switching between the different coordinates systems on your GPS is typically done within seconds, so if one set of coordinate system does not suit you, just switch to another. Make the gadget work for you, not the other way around.

Okay, I'll bite..

What happened?

I usually use MGRS due to where I get my maps (thanks old USGI buddies).

But as has been mentioned, I also wind up doing conversions. Many cell companies use different systems, but I do work for all of them. I always ensure I can work within all the systems. When we move into an area for work, I contact the local FD, EMS, PD, and Air Ambulance folks. One of the items I get is how they want their directions and GPS info. Cell sites are given addresses, but the address usually has very little to do with where it actually is, and how to get there.

I've seen the difference in datum as well. In the case where we found it- .10 mile in the area of a group hike.

From the air that's not a big deal. By foot in the woods - it matters.

I like UTM because the grid lines are frequent enough on the map you can find where you are. USGS quads don't have frequent enough lines to suit me. And then you are stuck interpolating between intervals of 2 minutes 30 seconds per line.

I've written about this on my website-
http://coloradowreckchasing.com/UTMesHiking/UTMeshiking.html

A lot of what I do has to do with ELT's. AFRCC gives us the coordinates as Decimal Lat/Long. Truth is as poor as the fixes are it is more of a general location to start the search, that a hard fix.

For most other uses UTM is the way to go.

I 'grew up' with UTM and prefer it. Problem is most geocaching and most run of the mill guidebooks run off Lat/Long.

While I prefer UTM, I am being forced by convenience to use Lat/Long system.

On top of this, maps come in so many different scales now that it's almost impossible to find a map at the last minute or with trail detail that matches the scales on my UTM card or whats on the base of my compasses.

I too ONLY use UTM-I tried the lat/long thing, and I simply cannot convert. I blame the Army...
Its hard to find topos in UTM, but I have a program that was given to me a few years back when I was on S&R that allows me to print maps in any scale I need, which makes it most convenient.

Another variable is who you NEED. My store is in Idaho. So I am interested in using the grid that will get me the most accurate and fastest response. Local agencies all use NAD 83/84.

I keep a scanner on at all times. I listen to all of the calls for rescues, accidents, marijuana fields and collared wolves. In most cases the people on the ground cannot communicate to the 911 operator or the helicopter on the way. In Idaho DO NOT USE UTM OR DEG/MIN/SEC. Do not pronounce the decimal point! Only pronounce the numbers - talk slow - they are writing.

The LIFE FLIGHT, NATIONAL GUARD, SEARCH AND RESCUE, DEA and the 911 dispatch all want you to read the location as -

"The accident is at 4396679 by 11618880"

I keep a window open in http://mapper.acme.com/

ACME comes up as -

N 43.96679 W 116.18880 MY FRONT DOOR

N 44.08265 W 115.82877 A WOLF DOWN

UTM for me. Much easier to work with. Only UTM downside I see might be for large area navigation, such a airplane pilots need. Lat/Long is more common for those folks. With UTM, you can look at two gridlines (either NorthSouth or EastWest) and determine the distance between them in meters. Simple math. You can't do that with Lat/Long. The distance between lines of Longitude differ, depending on what Latitude you're at.

I will use most any projected coordinate system to get along. Last few years while on continent I used the following:

NAD 1983 State Plane (FIPS by region). Sometimes use the 1927 State Plane system. For projection, I prefer the Lambert Conformal Conic Central Meridian of -91.33333333 with Standard Parallel of 29.30000000 & 30.70000000. My latitude of origin is 28.50000000. Geographic coordinate system of GCS North American 1983. Datum: D North American 1983.

I work in either meters or international feet. Sometimes work in US feet in north America. Back in the day, cotton rows.

Make real time adjustments for the wobble of the earth. In this regard, stay locked to particular stars for tracking.

UTM for land nav, Lat/Long for air or sea (actually any activity that will take you more than about an UTM zone of six degrees longitude.)

As others have said, UTM has a finer grid, easier distance measurements and easier callouts (unless you're straddling two zones, just need to read the easting and northing and you can drop the last two digits for 100m accuracy.)