Map Coordinates 101

**DSJohnson** · 09-19-2013, 08:56 PM

Really dates me doesn't it! LOL...Oh well. I have a serious question now

**DSJohnson** · 09-19-2013, 09:00 PM

If you are out in the wilderness with a map and a compass, what exactly do grids really do for you? I understand if you are using and dependent on a GPS but if you are just using good topos and you know how to use a compass what additional help is knowing/having the "grid coordinates" do for you? I guess if you were able to communicate and needed to be found it would help maybe? I am sure that I am missing some huge point and please feel free to show me the error of my ways/thinking or lack there of.

**Rick** · 09-19-2013, 11:58 PM

Actually, you pretty much have it. Most commercial maps like an Atlas have an alpha on the left hand margin and a number along the bottom margin. You can look up a city in the index and it will show it as G-7. You can then go to that approximate location to find the city.

On true grid maps, however, you can be a lot more precise. You will have numbers on the left margin and numbers on the bottom. These are typically six digit grids unless the map states otherwise. North (bottom margin numbers) is always stated first then East (left margin numbers). If the pond you are looking for is at 6,4 your precision becomes almost exact by looking at where in the 6 grid it lies. For example, it may be 3/4 of the way to 7 so the north grid may be 675. The east grid may only be 1/4 of the way into the 4 grid so your east grid becomes 425 (I hope that makes sense. think of it in decimals). So the grid for your pond would be 675425. Anyone looking at a map with the same grids would know exactly where that pond is. The rule of thumb is read right then up.

If your plan in a disaster is for everyone to meet at 750325 and everyone has the same map then they will know exactly where to meet. Everyone outside your family would be lost. They either won't know what you are talking about if they overhear your grid coordinates or even if they understand grids they would have to have the same grid map to know where 750325 is.

This is a bit crude but hopefully will give you the idea. On the map below read to the right 675 then up to 425 and there's your pond.

map.jpg

Now, I'm afraid, I must kill you.

**DSJohnson** · 09-20-2013, 12:15 AM

Thank you. In the big picture if things go south for just me AND I can call out it would be very simple to say I am at 750325 on Map XYZ but in a "worst case" scenario as far as land navigation goes, having grid coordinates on the topos is not essential. I can always tell the family to meet "at the big rock" IF we have done our pre-planing and are all in agreement about which big rock I am referring to. I have used the grids some just to learn how they work by doing a little (very little) Geo-Caching mostly to practice with the dang GPS but I trust my compass and map reading skills way more than I do my GPS skills anyway.

**Rick** · 09-20-2013, 12:33 AM

'Zactly.....but would be helpful over a very long distance, which most of us don't have to worry about.

**finallyME** · 09-20-2013, 09:26 AM

If you are just doing basic land nav......and you are able to follow terrain features fairly accurate....you don't need grid coordinates. I have taken many a hike, even long 30-50 mile hikes over many days with topos that didn't have grid coordinates. I do most of my hiking in the Rockies, and it is really hard to get lost if you have a good map and are paying attention. In fact, a compass is generally not necessary, just helpful in confirming where north is.

But, here is why I like grid coordinates on my maps....especially the UTM grid.

1. It helps you win or lose bets when you are betting with someone on your exact location on the map. One time I was 4 days into a 5 day hike and I was having an argument with the other leader in our troop as to exactly where we were. We both knew that we were on a specific trail, and we weren't lost, but we didn't agree on our exact position on that trail. Luckily, this map had a UTM grid overlay, and luckily one of the scouts had a gps with him. I asked him to pull out the gps and find our position, then showed how to find that on the map. It was a shame I didn't bet any money.

It was a good teaching moment though. Of course, this falls into the category that grid coordinates are useful IF you have a gps.

2. They are also helpful, if you don't have a gps, in doing back azimuths. This is mostly because they just provide more vertical and horizontal lines on the map that help with the angles.

3. They are helpful for me when I set up an orienteering course and specify grid coordinates. But, this is an example of forcing their importance.

**Ken** · 09-20-2013, 09:31 AM

Originally Posted by DSJohnson

If you are out in the wilderness with a map and a compass, what exactly do grids really do for you?

We used the grids for search patterns in SAR training and the real thing. A child or senior citizen goes missing in the state forest and the search is on. We even recovered a homicide victim once. The grids ensure that you're covering all ground and that you're not reworking the same area on your first sweep through. Like I said, the marshes and swamps were the worst, and we suited up and searched the ponds as well.