Fundamentals of Navigation for Adventure RacingPlotting CheckpointsAdventure races require you to pinpoint exact spots on the map and then find those places in the real-world. Each exact spot is called a "checkpoint" or "CP" for short. Most adventure races require you to plot the CPs on your map by using a pair of numbers, called coordinates. Coordinates are given in the UTM (Universal Transverse Mercator) grid system. An example of a set of coordinates that you may get would be: 405980/3316200. This pair of numbers tells you exactly where on the map the CP is located. So how do you find that specific spot?
Here's a map with the grid printed on it. We'll use this map to practice plotting a CP. To plot a checkpoint, you'll need to use the grid system that is printed on the map. You'll notice that there are numbers running across the bottom and top of the map at each one of the grid lines. These numbers get bigger as you go from left to right and are called "Eastings". They tell you how far east and west the checkpoint is to be plotted. The same thing is true for the left and right sides of the map. These numbers get bigger as you go from bottom to top and are called "Northings". They tell you how far north and south the checkpoint is to be plotted. Let's go through two plotting examples – First with a forward plotter and then with a reverse plotter.
Plotting with a Forward PlotterLet's plot the coordinate 405980/3316200 with a forward plotter. First, you need to determine which number in the coordinate is the Northing and which is the Easting. You can determine this by looking at the numbers you are given and comparing them to the numbers on the map. You'll notice that the numbers running from west to east on the map start with "40", so that means "405980" is your Easting and "3316200" is the Northing.
Now, you need to determine
which grid you need to be working with. Take the first 4 numbers in the Northing coordinate (i.e., "3316")
and find that on the left side of the map. Next, take the first 3 numbers in the Easting coordinate (i.e., "405")
and find that on the top of the map. Bring your fingers together to find the specific lower-left
edge of the grid in which the CP will be located. The map below shows this process.
Now, you have to find out exactly where in this grid the CP is located. To do this, put your plotter
card on the grid. And use the last 3 numbers in the Northing coordinate to find exactly how far up
and down in this grid the CP is located. Use the last 3 numbers in the Easting coordinate to find
exactly how far left and right in this grid the CP is located. The intersection of these coordinates
is the exact spot on the map where the CP is located. Move the plotter and put a dot on the map.
A Sharpie marker works well for this. The CP is located right on the windmill.
Plotting with a Reverse PlotterLet's plot the coordinate 406880/3314800 with a reverse plotter. You will follow the same first step as you did with the forward plotter. That is, use the first 4 numbers in the Northing (i.e., "3314") and the first 3 numbers in the Easting (i.e., "406") to find the grid in which the CP will be located.
Now, put your plotter card at the bottom-left corner of this grid.
Use the last 3 digits in the Northing (i.e, "800") to determine to how far up you should go in
the grid. To do this, slide the plotter card up the map until the coordinate you want is on the
bottom line of the grid. Now do the same with the Easting (i.e., "880"). You'll slide the card to the
right until the coordinate you want is on the left line of the grid. The hole in the reverse plotter
card is exactly where you put your dot to mark the CP. The reverse plotter takes a little getting used to. It requires you to re-think the serial order of the numbers on the card because they run in reverse order. However, it is much faster and more accurate than a forward plotter.
Calculating DistancesUSGS topo maps are marked in grids that are 1000 meters square. A lot of people make the mistake that the straight horizontal or vertical distance from one grid line to another on the map is 1 mile. Don't make this mistake! The straight horizontal or vertical distance from one grid line to the next is exactly 1000 meters.
Each one of the little squares on your plotter is 100 meters square. You can use your plotter
to measure distances on the map. Let's say you wanted to know how far it is from CP1 to CP2
on the map below. Put your plotter on the map with 0 at the spot you are starting (CP1) and run
the plotter to CP2. Now you can count the number of grid lines that it takes to get to CP2.
In this case it's about 450 meters. There has been a lot of usage of the metric system above. Yep... meters... you just have to get used to it. A meter is a little longer than a yard. There are 1000 meters in a kilometer (or "K" or for the military folks, a "click"). As mentioned earlier, the straight vertical or horizontal distance from one end of a grid to the other on the map is 1000 meters, not a mile. A mile would be 1.6 of those grids. If you go to a football field, this distance from the back of one end-zone to the back of the other is about 100 meters. If you walk one lap around the track that surrounds the football field, that's ¼ of a mile, which is 440 yards, or 400 meters. Here's a little table of conversions:
Go to the next Topic: Using the Compass Copyright 2008 by Ross Willis |
