Wednesday, January 21, 2009

Navigation - Grid References

Considering their importance in navigation, grid references are comparatively simple. First of all, what are they? Grid references are a numerical system of identifying a given point on a map. The numbers (when used with the right map) are applicable to only one area on that map.

A four figure grid reference will give a position within a kilometre square. This, though useful, is often too big. So generally navigators go further and use six figure references which brings the area down to a 100 metre square.

How do they work? There are a few rules to remember when using a reference. Get them right and there should be no more problems. The numbers, when referred to, identify a grid line on the map.

So first and foremost find the number along the bottom of the map and identify the grid line - Eastings. Then look for the number up the side - Northings. Run a finger up the vertical line and one along the horizontal line until they meet. That should put you at the intersection of two lines forming a cross. Now, which of the four squares do the numbers relate to ? This is the second rule. When using the numbers along the bottom look to the right of the vertical line. when using the numbers on the side look above the horizontal line, at the intersection.

The same rules apply to the six figure grid references. One additional rule is that the first column on the left is zero and the last column is nine. The bottom row is zero and the top row is nine.

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