Deriving Grid References From an Ordnance Survery Landranger 1:50000 map

Applications to the Environment Agency to introduce fish, fry or ova using form FR1 and to use fishing instruments (other than rod and line) and/ or remove fish from inland waters using form FR2 require the applicant to use six figure grid references. These enable the Environment Agency Consenting Officer to locate the fisheries in question. An example of a six figure grid reference on an Ordnance Survey (OS) map is TQ291796. This grid reference was derived from the Landranger map sheet 176 and marks the location of Buckingham Palace.

For mapping purposes, the Ordnance Survey has split Great Britain into 100 x 100km grid squares. Two letters, for example TQ, identify each of these grid squares. These are located in the four corner squares of each map and form the first part of any grid reference. This enables the map-reader to locate the relevant grid square to which the grid reference relates.

Each 100 x 100km grid square is covered by a series of grid lines spaced 1km apart. The vertical lines are eastings and horizontal lines are northings (Figure 1). They have numerical reference numbers. These form the second part of a grid reference, for example TQ2979, and enable the map-reader to locate the reference point into a 1km2 area (Figure 2). The easting grid line is given first, then the northing.

Each grid square is then divided further, by eye, through inserting 10 easting and northing gridlines, allowing the marking of the reference point to an accuracy of 100m. The position of the reference point in relation to these eastings and northings gives the final part of the grid reference, for example TQ291796. Again, the easting grid reference is given first, then the northing.

For more information on grid references, an online resource is available at http://www.ordsvy.gov.uk/.

Figure 1. Easting and northing grid lines on an OS 1:50000 map.