WeaponsMan-Learning Land Navigation: Second in a Series: The Topographic Map

Posted: April 1, 2016 by gamegetterII in Uncategorized

The best case is to have a map and a compass. If you have a general idea of the terrain you can navigate without either, of course. But if you have to choose one or the other, unless the map is complete crap, choose the map.

Why not choose a GPS? A GPS depends on things that you cannot control, including satellites (vulnerable to interception and destruction in wartime, and failure in peacetime) and the electromagnetic spectrum (vulnerable to jamming, meaconing, EMP and other QRM — manmade interference — and sunspots, areas of bad radio propagation (like iron-rich geological formations), and other QRN — natural interference.

Jamming GPS signals is child’s play, because (1) the frequencies used are fixed and published, and (2) a satellite is sending a very low-power signal from very far away.

A GPS also depends on something that has a knack for letting a guy down: batteries. GPS navigators and other smart devices are an update of the old pilot’s joke about a flashlight: something you put in your bag to hold dead batteries. (There are circumstances in which this joke is the very living soul of not funny).

What’s a Topographical Map?

A map is a graphic description of a physical place in (usually) plan view, meaning from an imaginary viewpoint overhead. There are innumerable kinds of maps. Planimetric maps are drawn to scale (of which more in a moment), show borders and boundaries, (usually) cultural features like roads, and coast- or water-lines. If you own a house or land, you have probably seen your lot on a planimetric map. A Mapquest street map page is a planimetric map (it’s also a thematic map, which is a kind of map that has a theme, naturally. Thematic maps can be planimetric, but don’t have to be).

A topographical map is a type of planimetric map that also shows the height of the terrain. How do you show the Z axis of the real world on a two-dimensional map? The convention for depicting height on modern topographic maps is to use isometric lines. That scary foreign word just means “same distance,” iso metric, see? So each height-depicting line on the map represents the same vertical distance as the others. This has some useful applications in the real world, which is where we want to use our maps, right?

Read the rest @ WeaponsMan  here


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