Mapping 101 - Part III - The Plot Thickens

Trout Whisperer posted on October 25, 2006 13:04 :: 8016 Views

Mapping 101 - Part III - The Plot Thickens

Now the PLOT thickens. With a very wide brush stroke I covered a map page and basic compass functions. Here comes the big picture. Acquiring a topo map of a perspective area.

For an initial choice scan some online topo maps at on-line map sources. There are many free ones to select from. By prescreening the area you can get some easy practice to build experience and confidence with. Prerequisites would be very open topography along an east west running road with one or two large terrain features within a quarter mile hike. It’s Just that simple.

My baseline compasses all come with a lanyard. It goes around my neck. It becomes part of the anchoring system for taking a sighting or shot with the compass. The needle only knows how to point (float) to north. (Karl proof) Someone a lot smarter than me made it so I cannot screw this up. I pick the degree of travel by adjusting the degree ring.

By laying out the map page and using some tracing paper (Mylar) you can with a pen or marker, and a baseline compass sketch out your first route PLOTTING.

This is done on your picnic table at home. (Outdoors away from any potential magnetic problems). This is your first one so we want to get off on good start. First orientate the map and compass to north. Your compass will show magnetic north and the map is grid north. By adjusting for the declination angle you will have… THE …North you need.

For example. This is an over simplification but I want to make it Karl proof. By using the map scale from the legend and measuring by rule with the baseline scale you figure at roughly 880 ft due north is a meandering stream running on a parallel to the east- west road your parked on. By checking the contours as laid on the topo map and scanning the map colors for the general topography you can insert mentally your pace count and start to dial in on a walking time for arriving at your meandering stream.

No matter how hard I try, I paddle at two miles per hour per day. On flat terrain I walk at fifteen minutes per mile before lunch with a lot of spring in my step. When you throw in crawling over logs or rain or snow or your dragging out one large sack of beaver traps you have to adjust on the fly. What you plan on the picnic table may not be what transpires in the field.

Your pace count is an estimate. The distance you scale on the map is an estimate. The degree you plot on the map is an angle out of a lot of angles. Basic compasses have 360 degrees to the circumference of the circle. In the army we had 6400 mils in the same circle. Tighter precision was the hope. So don’t be too critical when you do not arrive at exactly 16 minutes eleven seconds.

The tracing paper will give you a course to follow while you actually traverse the landscape. As you traverse the landscape check the topo map against what’s actually happening under your feet and in full view.3m tape will hold a transparency in place over the map page.
Along this hypothetical line I should encounter at approx 400ft from the road, a small knobby hill. Four hundred ft from the road I should have been walking for 16 minutes. When you hit the hill you check your watch against the tracing paper. Make your adjustments and note with the pencil. After three or four successful outings in a row you can round file the tracing paper because you’re hitting your stride and target.

In this first basic plotting all your doing is Dead reckoning, ( estimating a position by calculating , the distance, direction and amount of time traveled) the example was 880 ft for distance, direction was due north, we will allow 20 minutes for travel. Multiply by two for the walk back out.

Now we are 880 ft in the woods at the meandering stream. Time to go sightseeing or fishing. You follow the stream west for approximately 1000 ft. check your watch and watch the topo map. (Basically a left hand turn) Now its time to head back to the road. With map in hand, scan for any navigational nightmares. Dial due south and pencil in a time for your exit. When taking shots with a compass, always try to use the longest sight picture you can keep in sight. Little short shots of twenty feet tend to throw you off course. Long shots, less error. Pick the biggest tree you can identify at your furthest focal point. When you arrive, Spin 180 degrees and recheck your compass against the previous target. (Your back azimuth). This will help tighten your course or travel route.

With an angle and a distance we can move, with a compass we can get back home.