Understanding map scales and grids is key to making full use of your map
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Scales help us work out distance to our destination and therefore how long it will take us to get there. The smaller the area a map covers, the larger the scale is. So if you have a map on a square metre of paper and the scale of the map is 1:50,000 and another map on the same size paper with a scale of 1:25,000, the area covered by the first map will be 4 times the area covered by the second map. Every map will carry a scale, not just the value of say 1:50,000, but also a depiction of that scale. Here is the scale displayed on our Discovery series map.
Grids on maps serve a different function, they help to tell you, where on a map you are located. That could be because you have injured you ankle while out and about and you need help, or perhaps you found an interesting antiquity and you want to share that with a friend.
When taking a grid reference, always read left to right along the bottom or top of the map first and then bottom to top along the side of the map. This is particularly important in an emergency situation. If you want to precise in your grid reference, in your mind, roughly divide each side of the grid reference box into 10. That way you can give what is known as a 6 figure grid reference.
Discovery Series Map Grid
Let’s give a grid reference for Lugnaquillia with the following steps.
- Identify letter for 100,000 metre grid square in which the point is located. Grid Square T. The bottom left of each lettered square starts at 0 and goes to 100 in each direction. Each incremental square measures 1,000 metres on the ground.
- Quote the eastings. Locate the grid line immediately left of the point, read the large figures labelling the line either on the top or bottom of the margin of the map. Then estimate in tenths from grid line to point. Grid line 03 estimation 2. Eastings 032
- Quote the Northings. Locate the grid line immediately below the point, read the large figures labelling the line either on the top or bottom of the margin of the map. Then estimate in tenths from grid line to point. Grid line 91 estimation 8. Northing 918.
- Sample reference T 032 918 For local reference, letter may be omitted.
A Discovery series map will also give you centre of sheet coordinates in Irish Transverse Mercator (ITM) which is a newly derived GPS compatible mapping projection that is associated with the European Terrestrial Reference System 1989 (ETRS89).
Four-figure grid references
As we already said, when giving a four-figure grid reference, always give the eastings number first and the northings number second. An easy way to remember this is to keep in mind the letters HV (High Voltage), that is horizontal reading first followed the vertical reading.
In the diagram below, the number 4 is in square 28 across (on the horizontal) and square 54 up (on the vertical) and therefore, the four-figure grid reference is ‘2854’.
The other numbers in the squares above would get the following grid reference.
In order to be a little more precise with your grid references, you can give a 6 figure grid reference as shown below.
In the above diagram, we have taken the lower right square from the previous diagram and divided it by 10 in each direction. The pink circle is in the four-figure grid reference square ‘2552, but more accurately it is 2 tenths across and 7 tenths up within that enlarged grid square, therefore the six-figure map reference is ‘252527’. The red circle has a 6 figure grid reference of 257522.
Ireland is covered by the National Grid, that is the country is divided into 25 squares from A to Z (the letter i is not used). When you quote the six-figure grid reference you should put the letter of the area you are in before the numbers.
For example, the grid reference for Lugnaquillia, without the grid letter would read 032 918, but these numbers appear in every 100km square. The complete grid reference you should give to correctly identify Lugnaquillia would be “T 032 918”.
It is important to note that the National Grid reference is not related to longitude and latitude, even though these references are marked on the edges of our maps. Latitude refers to the north-south position of a point and longitude refers to the east-west position. It is a more universal and accurate way of referencing a point on the earth’s surface, used by satellites and GPS machines.