What Our Readers Are Doing (WORAD): Land Nav

compass-003Teaching the kids to navigate, inspired by posts in this blog:

It was probably months ago that I ordered a topographical map of our immediate area, and bought a modern compass to use with it. With my trying to finish the RR coach, my daughter’s wedding, and other things; I haven’t been able to get serious about the map reading lessons shared at the Weapons Man Blog.

We took the map out into the woods and hills a while back, to see if we could spot the terrain features on the map. That was fun, but this was more serious instruction. I ordered the map with magnetic north lines printed on it; so I didn’t have to compensate (azimuth?) 3 degrees for that. In the pictures below is the story of how our first lesson went, and a few other activities.

We’re humbled, and pleased. The navigation came out a little off — not enough to be off the map sheet, but enough to show how difficult dead reckoning navigation really is. Trust us that, with practice and care, one gets a lot better at it.

The terms used when compensating for the delta between magnetic north and true north are Variation and Declination. These vary by location and time and maps can display them by showing isogonic lines (on a large-scale map like a Joint Operations Graphic, good for planning D-Day, or an aviation sectional chart) or a Declination Diagram (used on small-scale, topographic maps). The Declination Diagram also shows you how to compensate for change over time (in the short term, such change is predictable, and so mapmakers incorporate the trend in the legend of the map). Large-scale maps don’t do this because they’re replaced more frequently — the life span of an aviation sectional chart is a few months.

It is possible to automatically compensate for the true-magnetic angle (or, if using a grid system, grid-magnetic angle) on Google Maps by using Google Compass by the private Barcelona Field Studies Centre. We can’t vouch for its security or likely longevity, and unlike a paper map and compass, you’re not going to have Google Diddly when the grid is down, but for now it’s a useful learning tool.

Go Read The Whole Thing™ (his vehicle-painting stuff is interesting, too).

9 thoughts on “What Our Readers Are Doing (WORAD): Land Nav

  1. Loren

    Sailors use the formula below to get the correct course.
    True
    Variation
    Magnetic
    Deviation (error in the compass due to it or it’s location such as near the engine block, etc.)
    Compass

    True Virgins Make Dull Company is the easy way to remember the steps.

    1. John Distai

      I’m assuming that blog is yours? I’ll start reading.

      I like the passage of “grab a kid” (and teach them something). I do that with mine. They aren’t interested in first, but then become engaged in it. Then my wife complains as she whisks them away to some passive activity performed by some other circus.

      1. Quill_&_Blade

        Yes it is. I guess I’m a creature of habit, for better or worse; a lot of the things I do require a skill level that’s beyond them, so I forget to get them involved where I can. But I’m getting better.

  2. Boat Guy

    I learned “True Virgins” long ago and expect that it’s still accurate.
    However the OTHER memnonic might not hold sway anymore
    Compass
    Deviation
    Magentic
    Variation
    True
    “Can Dead Men Vote Twice” – looks like we’re gonna have LOTS of “Dead Men” (and Women) voting more than twice in a couple of weeks

  3. Dave

    Magnetic north and true north are not the same. Magnetic north is in eastern Canada. You can find the declination at this site http://www.ngdc.noaa.gov/geomag-web/ Also, magnetic north is constantly changing. In Washington, our declination was 20 degrees in 2000 and about 15 degrees now, depending on location.

    As a Boy Scout leader, we use compasses similar to the Silva. I use this one which has a declination adjustment http://www.thecompassstore.com/51m3gl.html Unless you are using a surveying compass, accuracy is only about two degrees.

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