With UTM, you have different grids to choose among. there is NAD27, NAD 83, WGS 84 et al. I understand that the Coast Guard and other responders prefer to use Lat lon with a degree, minute, and decimal minute format - less ambiguity that way, since the same coordinate numbers plotted on the various UTM grids will give you different placements.

It is not hard to convert, but I leave my unit in lat lon, decimal minutes for those special occasions.....

A couple of quick comments regarding Datums and Coordinate Systems.

NAD27 is the older datum used in N American. Older USGS topo maps used this datum.

NAD83 is the current datum for newly published USGS topo maps. WGS84 is the default datum on most GPS units when they come out of the box. I believe all current nautical and aeronautical charts are published using WGS84. It is important to understand that NAD83 and WGS84 are functionally equivilent for us as map users. The difference is at most a meter or so anywhere in N America.

Coodinate systems such as UTM, US National Grid (a UTM variant), and the various versions of Latitude and Longitude (Decimal Degrees, Degrees & Decimal Minutes, Degrees & Minutes & Seconds) can be used with either NAD 27 or NAD83/WGW84.

However, a given coordinate in any system will plot to a different lcoation in NAD27 than it will in NAD83/WGS84. The difference in N America varies, but is usually less than a couple of hundred meters at most. For example, in Alaska the surface location of N 61 deg, W 149 deg 15 min in NAD83 is about 63 meters north and 118 meters west of the same Lat and Long in NAD27. (About 134 meters WNW.)

I know this stuff can get very confusing. The key things to remember is that for ordinary navigation purposes, NAD83 and WGS84 are the same. And the difference between NAD83/WGS84 and NAD27 is at most a couple of hundred meters. This is true in ANY coordinate system. As long as you set your GPS to the same datum as your map, you will be fine. If someone gives you coordinates of a particular location, make sure you know what datum they are using. A particular peeve of mine are guidebook authors who give GPS coordinates, but don't specify the datum!

To clarify, there is only one UTM grid, but as mentioned GPS's can use different map datum. You'll want to set your GPS datum to match that shown on the map you're using.

When using paper maps I highly recommend looking at maptools.com. Their tools - or similar map grids from other sources - make quick work of translating locations from a GPS to the map - and vise versa. When doing this I find it much easier using UTM coordinates, though to be honest I constantly find myself having to relearn how to use the grids on the map (might be some neurons damaged from my youth).

I'm a big fan of folks learning to use a paper map (good water resistant topo with UTM coordinates - I purchase mytopo.com maps), a baseplate compass with adjustable declination (set to point to true north - my favorite is the Suunto M-3), and a mapping GPS (set to match the paper map datum and displaying UTM coordinates).

Regarding GPS durability, so far every single one of my GPS units are still functioning - even my very old Garmin GPS III Plus and my Garmin Gekos, though their interfaces are archaic compared to today's units. BTW, I never rely on the GPS unit's water resistance! If you're concerned about batteries failing - make sure you buy a GPS that can use lithium batteries (less tendency to leak, better performance in cold, lighter weight) and bring along plenty of extras (a pack of 8 costs about $20). Oh, and the #1 rule is to set waypoints to my truck and other nearby key locations that will help me get unlost.

When preparing for an outing I use this website to convert Google Maps lat/lon coordinates to UTM:

http://boulter.com/gps/

My favorite book on this topic was GPS Land Navigation by Ferguson & Tucker, but like me it is a bit aged by now. Still, the key points haven't changed. I like that it emphasizes use of paper maps and GPS units TOGETHER, and it stresses practicing in your neighborhood before going out to more remote locations. I haven't kept up on the latest books available.

BTW, when using my car GPS (Nuvi) I use dd.dddd format lat/long coordinates rather than UTM. Faster conversion from Google Maps.

I tend not to worry about what coordinate system rescue crews use versus what I use since I likely won't be communicating with them. My objective is to not be lost, and if lost I can use my tools to get myself unlost again rather easily. If necessary (life at risk) I can use my PLB to get help and they'll receive the coordinates from the PLB.

Depending upon your application, the difference between NAD27 and NAD83 may be significant - not so much for most SAR operations, but critical to many archaeological applications.

At least in the lower 48, a lot of the topo maps are in NAD27. It is worthwhile to determine when the data on which the map was produced - maps currently in use for Channel islands National Park are based om aerial photography flown in 1943 (can't imagine why the military was concerned about mapping Pacific coastlines and islands in the early 1940's). the topography is still current, but cultural features - roads, trails, and buildings - are way out of date.

My experience is that trails shown on maps produced before aerial photography came into vogue show trails quite accurately, while those produced from aerial photos frequently mislocate trails.

So, don't just blithely trust the map. There is a lot of pertinent info in the fine print.

I think the bottom line is, work on your navigational skills and use the maps, GPS units, whatever to their full potential. I have taken the coordinates of my vehicle before launching out and I have been glad I did more than once - a worthwhile practice.

Well, yes and no. There is the basic UTM grid, which can use either datum. Then there are derivatives of UTM, notably the Military Grid Reference System (MGRS). Just to confuse things there is also the US National Grid (USNG), which some organizations encourage the use of. As an example of how these look, here is a waypoint in a park in Anchorage. First using NAD83/WGS84:

Lat/Lon= N 61 deg 12.047 min W 149 deg 56.712 min

UTM= 06V 341750 6788716

MGRS= 06V UN 41750 88716

USNG= 06V UN 41750 88716

The main difference between UTM and MGRS is that the MGRS substitutes a two letter code for the 100,000 meter grid square, which means that in MGRS coordinates Easting and Northing are always the same number of digits. Also, I've given the MGRS to 1 meter. Typically, they would be truncated to 10 meter or 100 meters, which just shortens the coordinate. Also note that for NAD83/WGS84 the MGRS and USNG are identical.

Giving the same location in NAD27:

Lat/Lon= N 61 deg 12.014 min W 149 deg 56.396 min

UTM= 06V 341866 6788571

MGRS= 06V UC 42029 88443

USNG= 06V UN 41866 88571

Note that the military uses a different two letter code for the 100,000 meter square when using NAD27, so the datum is explicitly encoded in the coordinate. USNG uses the same two letter code as it does in WGS84. Therefore with Lat Long, UTM, and USNG, one must specify explicitly which datum is being used. Also note that my understanding is that the military now uses WGS84 exclusively for all their mapping. Only older legacy military maps would have NAD27 and the alternate 100K grid square designator.

UTM and derivatives have many handy features. A nice square metric grid, "read right up", etc. However, some of these advantages don't work so well when one has to deal with areas that straddle two UTM zones (the 6 in "06V" above refers to the UTM zone). One of my pet peeves (besides not specifying datums) is navigation book authors who sing the praises of UTM, but never talk about issues associated with zone boundaries. But that's a topic for another long post!

I'm sure most of us know that for navigation purposes, there is no accuracy difference between NAD27, and NAD83. In the example above, all the coordinates refer to exactly the same spot on the ground. As long as you know which one you are using, you can choose whichever you want.

The only time datums are an issue is when you think a coordinate is in one datum, but it really is in another. Hikermor could give a coordinate in any datum he chooses, and I could find it, if I know the datum he used. However, if hikermor told me the priceless artifact was buried at N 61 deg 12.014 min W 149 deg 56.396 min (in NAD27) but I thought he meant NAD83, I would be digging in the wrong spot. If you take a waypoint with your GPS, you can just change the datum in your settings, and the coordinate will change appropriately. But if you manually enter the waypoint with the wrong datum, it will stay wrong even if you change the datum in your GPS settings.

What makes life interesting is the situation where your organization has decided that GPS coordinates will be referenced to NAD83, but all the existing maps are NAD27. Ah, well, the conversion isn't that hard.

But I think this explains why some outfits prefer Lat Lon.

From personal experiences, when everyone is squared away and consistent, the systems work beautifully. I walked right up to some significant stuff recently, with absolutely no problem - and a difference of even five meters or so would have complicated matters.

AKSARR, thank you so much for giving me a way to keep you from finding (and presumably removing) our priceless artifacts. Gotta keep them pot hunters at bay!!

I've not taken the time to understand the difference between all those different grid systems. I struggled to make lat/long work well. When I learned about the UTM system I was amazed by its ability to related to useful distances - certainly within midwest US sight distances.

Still, like I said, since I don't use UTM coordinates on a regular basis so I find myself relearning how the grid's easting & northing grids work, so I keep going back to maptools.com's turorial to remind myself. I never seem to remember which direction the 1000x1000 meter grid runs - which corner they start at - even though it works just like an X-Y regression plot. Hmmm, maybe that will help me remember.

I think the roamer type grid tool might have caused my confusion, since they tend to be used kind of backward - with the 0,0 point at the target location and counting down & left to the grid boundaries.

Again, I've come to really appreciate maptool.com's tools and especially their explanations & tutorials.

By the way, mytopo.com's topo maps can be ordered with either "Standard NAD83/WG84" or "NAD27" datum, and they can be ordered with no grid, tic marks, or full grid lines for either lat/long or UTM/MGRS/USNG.

The topo maps are printed on waterproof paper with fade-resistant waterproof ink, and they can be shipped folded or rolled. They can also be ordered laminated. The paper feels kind of plastic-ish to me.

I agree that they are pretty aged and wish they could get updated a bit. For the Boundary Waters (Minnesota+Canada) there are companies that maintain and sell more detailed & updated maps, but they use a different map scale, thus they need their own map tools (which maptools.com sells). I like this supply & demand sort of model (avoiding politics here).

Sorry if this sounds like an ad for mytopo and maptools, but I like their product(s) and especially like the choices they provide.

One of the reasons I like using a GPS with a paper map, and have a somewhat lesser focus on using a magnetic compass, is that in many midwest forested and wetland areas it becomes almost impossible to walk a straight line compass bearing (or is that an azimuth?). I fully suspect that the same thing happens in not-so-flat terrain.

I've read about and tried to use the classic methods for overcoming such issues, but struggled. A GPS with a built-in compass has the ability (somewhat miraculous to me) to continually point to my desired destination - and provide a distance to the destination - from anyplace on Earth.

I know that there is some level of GPS inaccuracy and there is the ongoing reality that the GPS could simply fail to function, but to me the capabilities are amazing. Still, it would be foolish to not bring a compass and not know how to use it with the paper map. If nothing else the compass allows me to turn off the GPS (save battery power) and still head in the prescribed direction.

I can imagine a day when a smartphone can be made rugged and waterproof enough that it will truly replace a GPS - even for use where cell service is not available. It's probably not that far off.

Nearly all of my hiking has occurred in not-so-flat terrain which i relish. Walking in a straight line if often (usually) irrelevant.

You need to figure out the best route from A to B and that is where to topo map is a huge benefit, indicating where cliffs are present, the possible location of waterfalls and similar obstacles.

As a rule of thumb where I travel most, going uphill, you follow the ridges; going down, take to the valleys and canyons. There is also the question of the vegetation you must penetrate, which will often influence your decision.

All in all, the best route is rarely a straight line, following a compass heading.