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How Far is it?

How far is it, Introduction

The Ordnance Survey originally mapped out the U.K. in miles and feet, longitude and latitude. Now Ordnance Survey maps are in metric, and include the National Grid, allowing reference correct to within 100 meters. I am slowly including the Grid references for all the places named in the Gazetteer.

The National Grid divides Great Britain into 100 km squares, giving each of those squares a two letter identifier. The westernmost 5 km of Coigach is in "NB", the rest is in "NC". Below NC is the square that includes Ullapool, that square is "NH".

A source I have used for the Coigach Gazetteer file is the 1976 Ordnance Survey, Sheet 15, Second Series, titled "LOCH ASSYNT". It's scale is 1:50,000. The map has a light blue grid overlayed, dividing the 100 kilometer blocks into 1 kilometer squares.

The Ordnance Survey has recently put its own Gazetteer back on line! It has a very fast search engine, and covers all the U.K. Unfortunately, though it is based on the 1:50,000 map, it omits many of the smaller Coigach features, and it shortens grid referances to 1 kilometer accuracy. Still a great resource though; Ordnance Survey Gazetteer

This file links from my Coigach Gazetteer file, and is one of a growing number of files dealing with Coigach, visit my introduction file at "Some Coigach Genealogy" for descriptions and links to the others.

If the following techno-babble gives you any trouble, email me!

Donald MacDonald-Ross

Calculating distance, using the National Grid

With the help of a long dead Greek guy called Pythagorus who probably never got up to Coigach we can calculate distances between places using the National Grid!

To start with, lets pick two places in the same 100km block; Achiltibuie at NC 025 085, and Culnacraig at NC 066 035.

Each three digit group of numbers represents a distance first east, then north of the south-west corner of the 100km block. Three digits represents an accuracy of up to 100 meters, so to simplify things later, complicate them now, by adding a "00" to the end of each group, and eliminate any leading zeros, i.e;
025 = 2,500
085 = 8,500
066 = 6,500
035 = 3,500

You might want to break for a coffee about this point, clear your head, curse me, then reread the above!

All the groups now represent distance in meters north or east of the start of the 100 km block (Block NC in both these cases).

Now, subtract the smaller of the first groups from the larger of the first group;
That represents the difference east-west between the two places, in this case four thousand meters (4 km).

Repeat for the second groups to find the north-south difference;
(five thousand meters, or 5 km)

At this point Pythagorus steps in, and says (in ancient greek); "the square of the length of the hypotenuse of a right angle triangle is equal to the sum of the squares of the other two sides". It does sound better in the original language of course!

The distance between the two places on the map represents the hypotenuse of a right angle triangle, with the east-west and north-south distances representing the two sides. So square those two measurements, add the squares, then find the square root of that sum;
= sqr root of ((4,000 X 4,000) + (5,000 X 5,000))
= sqr root of (16,000,000 + 25,000,000)
= sqr root of 41,000,000
= 6,403.1242

Remember that the original Grid References were only accurate to within 100 meters, so round your result, in this case to 6,400 meters, or 6.4km from Achiltibuie as the preachan (gaelic for crow) flies!

If you need the distance in miles, multiply the kilometer distance by .6214, in this case;
6.4 X .6214 = 3.98 miles

Crossing 100 km boundaries

This is more complex, but the principle is the same. Basically, grid reference repeat every 100km block, and so you simply place a "1" in front of the east-west measurement for the reference in a block east of the block that has the other reference. Similarly, add a "1" in front of the north-south measurement for the reference in a block north of the other. Then do the math as above.

This works for adjoining 100 km blocks, if the places are two blocks away, change the "1" added above to a "2". Three blocks to a 3, etc.

This file, and others dealing with history and genealogy of Coigach, links from my homepage at:

Any suggestions for additions or edits please feel free to email me,

Donald MacDonald-Ross, at:

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