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Tuesday, February 16, 2010

Urban Survival Skills - Map Reading #3, Determing Distance and Azimuth

When "Bugging Out" from your home to your safe location, you may be forced to move over land on foot and if so then you'll need the ability to plan a route, measure distance and determine compass azimuth or heading in order to make that movement(s). Besides, map reading and rudimentary land navigation are excellent Survival Skills to add to your Urban Survival Skills kitbag.

Determing Distance on a Map. Determining distance on a map is done using a straight edge, like a piece of paper, then measuring on the map and determining distance by the map scale found at the bottom of the map. Place a straight edge of paper on the map and mark the area, from (location A) and to (location B), you want to measure with tick marks. Match up the tick marks to the distance scale on the bottom center margin of the map with the distance you desire the measurement in.

You'll be measuring in straight lines or a series of straight lines because your planned route will very rarely be a straight line due to terrain considerations. Ensure you measure small portions of "legs" of your route and add up all the legs to obtain the total distance needed to travel.

Determining a compass heading or azimuth. To be able travel across country from where you are to where you want to go, you'll have to be able to also plot the compass heading or compass azimuth. Following a compass heading or azimuth is called "dead reckoning".

To plot a grid azimuth on the map, draw a straight line from where you want to measure the azimuth from to the location you want to measure the azimuth to. Place the index (center) of the coordinate scale (also called a protractor) on the starting point, ensure that the coordinate scale is lined up with the grid lines on the map, then determine azimuth using the degree scale.

Converting Grid Azimuth to Magnetic Azimuths. The measured azimuth determined from one point to another on a map to is called a grid azimuth. It is going to be different than a magnetic azimuth or what the same direction would be using a compass.

The Declination Diagram on the map makes it easy to determine how to convert azimuths from grid to magnetic or magnetic to grid.

Grid to Magnetic. If applying a Grid azimuth from a map plot so that a compass bearing can be utilized then you must convert the Grid azimuth to a Magnetic azimuth.

Magnetic to Grid. If applying a magnetic azimuth from a compass bearing to the map you must convert the Magnetic azimuth to a Grid azimuth.

Another method, in the absence of a declination diagram to determine magnetic azimuth or the compass heading, is to orient your map to magnetic NORTH by aligning the map towards compass NORTH, the laying your compass along the route from where you are to where you want to go and read the magnetic azimuth.

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