Measurements and Accuracy

Now that I am mapping boulder fields I thought I would describe the process of how I measure the distance between boulders and place them on the field notes. This process works for anything that needs to be measured.

I use a metal ruler, six inches long, with one edge metric and the other in inches. (Take a compass with you when you buy your ruler so you can pick one that is non-magnetic.) The first thing you do is take some blue painters tape and mask off the inch edge of the ruler. Nothing is worse than using the sixteenths by mistake when you want millimeters. Been there, done that, wore out an eraser.

Know your pace count per 100 meters. Not the running pace count that orienteers use, but walking at your mapping stride. Mine is 61 double paces (count only the left foot) per 100 meters.

Make a simple chart with paces in one column, millimeters (at your map scale) in one column, and meters in a third column. I print out my chart and tape it to my map board. Here is the chart I use. You can look at the formulas and see how I calculate everything.

Now how do you use it? Starting from a boulder that you have already placed correctly(!), count your paces to the next boulder. Use your chart to convert that to millimeters. Use your ruler to measure the distance on your map and make your mark (in the right direction, of course).

You can also use the chart to convert from meters to map millimeters. I sometimes carry a laser rangefinder, which can save a lot of steps. Instead of pacing to the next boulder, I use the gadget to tell me the meters, and convert that to map millimeters using the chart.

Why does the chart round off the millimeters to 0.5? Because you really can't make a pencil mark smaller than that, and more accuracy is not always a better thing.