GPS + UTM = GOOD IDEA

If you don't use the UTM system on your GPS reciever, you have no idea how much more of a simple and effective system this is than the old lattitude/longitude method. This is especially the case with Topo maps, which have UTM coordinates printed right on them.

For what it is worth - there is a BIG movement in emergency services to standardize on the UTM system - it's officially called the US National Grid (USNG) and the "Datum" (sort of like survey data) to use is NAD83.

basically, with UTM, you have a simple "sector" like number and then two long numbers that give your position in meters within that sector. No "North Lattitude" no decimals, no minutes, no seconds - just a sector and a set of numbers that puts the crosshairs on your position on the map.

there's many great files on the internet on the subject.

Careful Martin, you'll get Benjammin stirred up and waving his divining rods and rules of sine. <img src="/images/graemlins/grin.gif" alt="" /> <img src="/images/graemlins/grin.gif" alt="" /> <img src="/images/graemlins/grin.gif" alt="" /> <img src="/images/graemlins/grin.gif" alt="" />

No offense, Benjammin. Just kidding. <img src="/images/graemlins/smirk.gif" alt="" />

Actually, Martin it is not a LONG list of numbers. As an example, to borrow from John Carnes book on www.maptools.com, consider the following:

An abbreviated format for a set of coordinates would look like:

59 82 Describes a 1000m by 1000m square.
597 821 Describes a 100m by 100m square
5974 8218 Describes a 10m by 10m square
59741 82182 Describes a 1m by 1m square

You are right. It sure beats figuring longitude/latitude.

I sat down this evening and learned UTM in about a good hour. It's great.

I would also like to thnk Martin for very kindly answering my many dumb questions about GPS. He IS the man.

Just remember to match your datum on your map to the one your GPS is using. There is a large discrepancy between WGS84 (which is the default on my last two garmins) and say NAD27 or Tokyo or whatever your map has in the marginal data.

Garrett

Do you have a strong opinion as to which north to set the GPS to?

Some units give a choice of grid north, magnetic north and true north. And some people recommend you set it to magnetic north so it matches your compass. However, I am currently persuaded it is better to use grid north. Then the GPS and map are in perfect sync. If you care about magnetic declination (or whatever you guys call it), you will be used to correcting it for the map so you can correct it for the GPS as well.

I am writing from the UK, where the Ordnance Survey grid is well-established. Just about all the larger walkers maps are derived from OS maps and have the OS grid, and are very easy to use with GPS. I believe most road maps are the same, although it is worth checking before buying a UK road atlas.

I use true north rather than magnetic north. But then again I only use compasses that have adjustable declination, so that they too are set for true north.

One potential problem with this coordinate, it is actually reapeated 60 times around the world. That is why in MGRS a coordinate will usally include a zone.
Like 12S 34765 24576, that would represent a 1x1 meter square unique to grid zone 12S, not repeated again. The reason the military uses the full number is they can be in the middle east and be talking to someone in N. Carolina, the person in NC cannot mistake the position to somewhere 20 zones away. Hope that made sense:) Just a thought!

Grid or local magnetic. True north is less useful excepting over longer hauls.

Martin - maritime vs. land?

My maritime work is tytpically inland (lakes and rivers) and so UTM and Grid North is the way to go.

I'm working now on some more localized mapping of lakes and finding that true north is really less of an issue than where you are and where you need to go.