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Apr 16

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Basic map reading

 

Basic map reading knowledge is fundamental for surviving in nature

Basic map reading skills include interpreting maps by understanding contour lines, scale, grids and magnetic variations on direction

 Reading the signs

Before embarking on any expedition you will have learned all you can about the terrain, equipped yourself with maps and worked out routes. Memorize the lay of the land, which is not the sexy blond Swedish girls that you may find frolicking in the waterfalls either. By the lay of the land, we mean stuff like rivers, prominent features, hazards and even expected weather conditions-all of which will be invaluable if you find yourself in difficulties. In choosing a camp site, tracing water and finding the other necessities for survival  you will need to know how to interpret the surrounding countryside.

Maps

Basic map reading requires that you choose maps carefully, making sure that they are to scale that will be useful to you and show helpful information. A very large scale map that shows every footpath and building will be of no use at all if you are driving say 1000km along a motorway. Everything will be shown in great detail, but only a tiny fraction of the journey will appear on one sheet which means you would need to pile your car with maps and change from one to the other every few kilometres.

basic map reading

Maps and terrain

height cannot be reproduced on flat sheets of paper so altitudes are recorded at regular intervals-usually between 20m and 50m-and every point of the same height is joined by a line-the contour line. In most cases lines join up to form a complete shape, some sort of irregular oval with bulges here and there. If they suddenly stop against another line that means that there is an abrupt change of height-in fact a cliff or a very steep fall.

In basic map reading, the only contour line you can see in nature as that of sea level along the coast ( even that is not quite true because of the tidal variations) but you can imagine the contour lines as the edges of flat disks and that these are ranged equally above each other. If you threw a cloth to rest over them it would link them together in a shape that would be approximately like a hill or other feature. However, you do not have a record of exactly what happens between contour lines and there will not necessarily be an even slope connecting them. There could be outcrops of rock within the 50m variation.

Basic map interpretation

The intervals between the contour lines are the distances between horizontal points at the same theoretical height-not the actual distance on the slope of the ground. They are measured in units that show relative positions and are not to a scale as is the horizontal plotting. It is a common error to think of a group of contour lines indicating a rise in the ground comparable to the scale of the distance shown between them-but the scale of a typical hikers map is 1:50000 and 10m on that would be only 0.2mm. Contours spaced 5mm apart on the surface of the map would be at a horizontal distance of 250m and the gradient only 1 in 25.

Scale of maps

Before you start to use a map, you must understand its scale. This may be shown by a scale bar marked in kilometres to the size that they are shown on the map or it may be given as a ratio-1:50000 means that every measure on the map represents a distance 50,000 times greater on the ground.

Key of maps

Basic map reading involves the understanding of the keys and symbols used within the map to represent natural and man-made features-rivers, roads, swamps, trees and so forth.

basic map reading

Grids on maps

Maps always show a grid of lines which divides them up. Usually based on degrees latitude and longitude. These allow you to assess distances based on ground measurements. They are also used to find your location. Your position is a coordinate made up from the line references from 2 adjoining sides of the map. Dividing the latitude and longitude into smaller sections will give you a more accurate position. This is key as you would need to break the coordinates not only into minutes, but seconds as well. getting this wrong could mean a difference of 200m in your positional plotting.

Local magnetic variation

Lining the compass up with the grid lines on the map, you can work out the magnetic variation which most maps display in the ‘key’ area of the map. When hiking on magnetic bearings, always remember to account for the variation.

 

 

Permanent link to this article: http://blog.souladventures.co.za/2014/04/16/basic-map-reading/


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