The scale of a map is the relationship between distance on a map and the distance on the ground.
In Ireland, the scales we most commonly use are 1:50,000 and 1:25,000. Other scales we may encounter less frequently are 1:30,000 and 1:20,000.
On a 1:50,000 map, 1mm represents 50,000mm on the ground and on a 1:25,000 map 1mm represents 25,000mm on the ground.
We can use a ruler to measure on a map but also the left-hand side of our compass has a built in ruler in mm.
While the numbers may seem daunting, there is a very quick way to convert a map measurement to ground distance.
Since there are 1000mm in each metre we can ignore the thousands and think of the scale as being 1 mm on the map = x metres on the ground.
1:50,000 is therefore 1mm :50,000 metres
1: 25,000 is therefore 1mm :25,000 metres