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OS Grid References

For recording to provide effective data for local purposes, such as planning and conservation work or national analysis of how particular species are faring, records have to be related to sites and locations.

The grid reference for any butterfly or moth record should be to at least 1km square accuracy (four-figure grid reference), and preferably six-figure references which pinpoint a sighting to a 100m x 100m square.

Data is plotted in summary form on distribution map e.g. as tetrads (2km squares) for local maps, or 10km squares for the national scale.When it comes to mapping, this data is plotted in summary form on distribution map e.g. as tetrads (2km squares) for local maps, or 10km squares for the national scale (see map left).

Generally atlas organisers seek to ensure that some recording is carried out within each tetrad or 10km square, to give a good level of mapping coverage.

Using Ordnance Survey Grid References

Please use National Grid references from Ordnance Survey maps - not road maps, which may have non-standard grids.

1km squares are marked by a grid of light blue lines on 1:50,000 series (Landranger) OS maps. The grid reference of a 1km square consists of the 100km square code (e.g. SP), which will be marked somewhere on the map, followed by four numbers, which mark the bottom left-hand corner of the square.

Ordnance Survey Landranger Maps which cover the Warwickshire, Coventry and Solihull area are numbers 139, 140, 141, 151, 152.

Find out more about Landranger Maps on the Ordnance Survey web site.

Use Our Mapping Tool

Our interactive Mapping Tool which was added to our web site in 2009 allows you to visually find the location and automatically generate a grid reference for you. You can also toggle between aerial photo images and zoom in to accurately pinpoint your sighting within a 10m accuracy and generate an 2, 4, 6 or 8 figure grid references. Just follow the instructions provided.

Many thanks go to Keith Balmer for sharing the code for this mapping tool originally used on the excellent Bedfordshire Natural History Society web site.

Example Grid Reference (SP482937)

The first two numbers of a grid reference refer to the horizontal (East-West) scale and the second two the vertical (North-South). It is very important to put these in the right order.

A 6-figure (100m square) grid reference is derived by dividing the 1km square into tenths, from the left (west) and the bottom (south).



For example, the map reference of the cross in the shaded square illustrated above is given by combining the east-west reference, 482, with the north-south reference, 937, giving a full reference of: SP482937.

When you move into another 1km square, record sightings there separately, so that important sites can be correctly identified. If you do not have access to suitable maps or are not familiar with grid references, please do not be put off from recording the butterflies which you see. Contact your local coordinator and they may be able to help.