Each OS map has a large letter outlined in blue printed on it. This indicates the sub- zone from which the map is taken. If an OS map covers more than one sub-zone, the letters of each sub-zone will be included.
Identify the sub-
zone letters on this map fragment. Referring to figure 3, which part of Ireland do they indicate?
In order to successfully identify features on an OS map, each sub-zone is divided into smaller squares by a grid of blue lines.
The vertical lines (up and down) are Eastings. Their values increase towards the east. We read them across the map in an eastwards direction.
03 56 57 58 59 60 61 03
02
02 01 01 00 56 57 58 59 60 6100
„„Eastings and Northings are numbered from 00 minimum to 99 maximum. „„We read Eastings first, then Northings.
A common error with Northings and Eastings is to think that Northings must point north. In fact, Northings do not point north – they increase as they move higher north. Remember Northings and Eastings by remembering that Northings do not point north!
Grid References on an OS Map
When locating a specific location on an OS map, grid references are used. There are two types of grid references: four-figure grid references and six- figure grid references.
Four-Figure Grid References
Four-figure grid references are used to give the location of a single square on the OS map, so they give the general location of features within that square.
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The horizontal lines (across) are Northings. Their values increase towards the North. We read them in a northwards direction.
