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exbiologist's picture
Location: Colorado
Joined: 09/19/2008
Posts: 2397
Navigation Help

It seems there are a lot of folks who do not know how to use half the features provided by their GPS or map. Beyond marking points and then using the “go to” function, there are several things people should know when attempting to navigate.
First of all, switch your GPS units to UTMs. In my Garmin, it’s called UTM UPS. Without getting overly technical, UTMs are a simple X-Y grid system placed over the earth. Because the unit is in meters, it becomes much more logical to use than decimal degrees, or degrees, minutes, seconds. The only way to calculate your position on a map with decimal degrees or degrees, minutes, seconds are with special rulers that few hunters own, nor know how to use, unless they were in the military. For the Average Joe, with a high school-level math skills, UTMs make more sense. Here in Colorado, our coordinates are projected in either Zone 12 or 13 which is a way of refining the accuracy of mapping a 2-D system onto the 3-D earth, usually in map datum NAD 27 (it will say on the corner of your map). But don’t worry about that for right now, unless you’re manually inputting coordinates into your GPS. The first set of digits are called Eastings. Here, they are six digits long, but in reality they are 7 digits, because they start with a zero. This number represents how far east or west you are from the central meridian. The 7 digit Northing is how far you are from the equator, all in meters.
But who cares about that? You should, here’s why. Let’s say you’ve been wandering around hunting and don’t know where you are. You marked your truck on the GPS this morning, so you could get back by simply following a straight line, regardless of what it leads you through. Wouldn’t it be better to know exactly where you are and what you’ll be walking through or whether there is an easier way around to your vehicle? What if you wanted to investigate a terrain feature, whose coordinates you hadn’t previously entered into your GPS? How would you go about doing that?
The vast majority of maps these days have UTM grid coordinates marked on them. They are typically in 1000 meter grid squares or hash marks. For instance, on the National Geographic Trails Illustrated map I am looking at, the numbers on the top, called eastings begin with a superscript 3, followed by two normal sized numbers, on the side of the map, the superscript has two numbers all beginning with 43, followed by two normal sized numbers. So, let’s say our GPS says we are at 0302465E 4317521N. Where is that on the map? Remember these are 1000 meter grid squares. So on the top, the eastings, follow the superscript 3 until you hit 302. What about the rest of the numbers, the 465? That means you are 465 meters east of the 0302 gridline. Basically, within 35 meters of dead square in the middle between grid lines 0302 and 0303. Now, for the northings, 4317521. On the side of our map, we should see a grid line for 4317, then we continue 521 meters north of that line, which once again, puts almost in the middle between the lines for 4317 and 4318. Where those two lines intersect is your position. Understand?
Using that same system, you can also manually enter coordinates into your GPS to navigate your way to a terrain feature.
Many guys these days also don’t know how to properly use a good compass. A good compass has a rotating dial, not a simple north arrow.
Two quick and dirty uses for your compass: staying on a course, or determining a on bearing. How do you do that, and why, especially if you have a GPS?
Let’s say our GPS indicated which direction to head and it was through the timber to our meadow. I don’t know about you guys, but I’ve always had difficulty maintaining satellite reception in heavy timber. Your GPS pointer will tell you which direction the waypoint is, but it might not have a good fix on your location, giving you inconsistent directions. So you stop, letting the satellites find you again and the GPS tells you the direction you need to head to find your meadow, but you know you’ll lose reception as soon as you move. Many GPSes will also give you the direction in degrees. 0 is north, 90 is east, 180 is south, 270 is west. Your direction dial says 45 degrees, northeast. How do you stay on that course? Whip out the ole compass, did you ever notice there is one white arrow, one red arrow? And a red outlined arrow on the dial opposite of the white arrow? We want to go 45 degrees, so rotate the dial to 45, or northeast. Then turn your body or compass so that the red arrow overlays the red outline, that is the rough direction you need to head.
Same idea if you are trying to figure out what direction you are heading. Keep facing that direction, with your compass out in front of you. Rotate the dial so that the red arrow and the red outline overlay each other, then read the indication.
GPS isn’t working? One other use for your compass is to take a bearing. For the moment we will not worry about declination, or how true north and magnetic north differ slightly. Want to triangulate your position on a mountaintop. Take a precise bearing of the prominent peaks listed on your map, then use the compass to help you draw a line back towards your potential position. Do the same thing with two or three other peaks to create an error polygon. You should be somewhere with that polygon. That is the basics of triangulation, and similar to how satellites calculate your position.
I hope this helps somewhat. And hopefully I didn’t leave out anything crucial.

Bull Buster's picture
Location: Nebraska
Joined: 10/12/2007
Posts: 167
Navigation Help

very good info. thanks

Location: Utah
Joined: 02/24/2003
Posts: 591
Navigation Help

Great info and thanks for posting.

One tip though I ended up buying a topo map on DVD for my state and simply by moving my mouse pointer around on the map it does display the GPS coordinates of the location of the pointer. Long story short I am easily able to find my decimal GPS coordinates on my topos that way and able to enter in the coordinates from a map to my GPS. Just a thought.

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