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|Thanks for you cle.. by dewsbury (Show all posts)|
Map coordinates of Djouce.The majority of maps in Ireland such as the OS/ LPS/ Harveys/ Healy etc use a system such that a place is represented in this style A 123 456. All GPS units and all books I have seen use the same style for representing the Irish Grid. The "A" represents one of 25 squares that cover the island each of 100km by 100km. The "123" represents the easting within that square or the distance from the left edge, in this case 12.3km The northing represents the distance from the bottom of the square, in this case 23.4km
So any point on the island can be represented to within 100m with just 7 characters. Djouce for example is O 178 103 (that is O for Oscar, followed by 6 numbers). For greater accuracy you can extend the number of digits in the easting and northing, so for example a more accurate position for Djouce is given on the website as O17858 10360, which represents a point to within 1 metre.
While East-West maps have a number of useful characteristics, regrettably they have chosen not to use this well established convention and instead of using the 100km squares mentioned before, use a distance from a point off the south west coast. The point is known as the "false origin". In that system Djouce's coordinates of 3178 2103 means 317.8km east of this point and 210.3 km north of it. You will note that the "178" and "103" are the same digits as appear in the conventional grid reference.
At least some of the East West maps do show the letters that the conventional system uses in a little inset towards the bottom left and you could, with some effort, figure out what the letter should be. (The letter is known as the myriad letter incidentally.) However you may find it easier to use one of the other types of maps to work with grid references and GPS units.
Another advantage of the other maps is that they show the eastings and northings on the grid lines at intervals across the sheet. This is advantageous because when the map is folded it makes it possible to work with grid references. For any East-West map I have been able to check this is not the case, which is extremely awkward. For example to go from a GPS reading on say a Garmin GPS you take the figure from the GPS which might be O17858 10360 and first remove the last two digits of the easting and northing which is easy enough but then you need to figure out what figure to put in front of the easting and northing based on the myriad letter, a process which of course is error prone. You then need to unfold the map completely to be able to see the easting and northing printed at the side of the map and only then can you figure out your position on the map.
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