Teaching 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).