![]() ![]() Read full details on how to read grid references. Cambridge University Library is a legal deposit library and so, with the exception of some maps at the oldest and most detailed scales. Maps have been published at a variety of scales showing varying amounts of detail. TF73G - identifies tetrad G within 10-km square TF73 Ordnance Survey (OS) is Britains National Mapping Agency and has been making maps of England, Wales and Scotland since 1791. TF722336 - identifies a point to the nearest 100 m Enter a location search below to zoom to the approximate location. H64 - identifies a 10-km square in Ireland (occasionally written as IH64) Instructions: Simply right click on the map to find a grid reference at that point. Correct examples of grid references are: TF73. All British grid references should begin with two letters, those in Ireland starting with one letter, and followed by a series of numbers (and/or the tetrad code). A correct grid reference does not include the map sheet number. TF73 - identifies a 10-km square in Britain Correctly reading grid references is crucial for many BTO surveys. Reading grid referencesĬorrectly reading grid references is crucial for many BTO surveys. A transparent overlay for the Landranger maps showing a 10-km square and tetrads was available on request during the Atlas survey period. ![]() In Ireland the Ordnance Survey of Ireland Discovery Series (1:50,000) maps are most useful. Ordnance Survey Landranger maps (1:50,000) or Ordnance Survey Explorer maps (1:25,000) are perfect for this purpose. Part of the fun of Atlas projects is poring over maps, deciding on the best route to take you past this pond, or that promising-looking wood. We strongly recommended you got an up-to-date map of the area you proposed to survey. Read more detail on giving complete grid references. A tetrad is then given its full reference as the 10-km square code followed by the tetrad letter (e.g. There are 25 tetrads within each 10-km square and these are labelled A to Z, excluding O (to avoid confusion with zero), from bottom left (SW) to top right (NE). ![]() A tetrad (from the Greek tetras meaning four) on the other hand is a collection of four 1-km squares arranged into a 2 km by 2 km square. A 10-km square as its name suggests is a square 10 km by 10 km. Ask pupils how we know that we have found the summit. The summit of Snowdon is located in grid square 6054. Snowdon: First find the summit of Snowdon. A key is available from Ordnance Survey website. There are various scales of resolution, but for the Atlas we worked with 10-km squares and tetrads. Then, using the extract from the OS Map Extract, or copies of the map itself, work through the maps skills detailed. A single map projection (Transverse Mercator) covers the. Like many bird surveys the Atlas used the Ordnance Survey National Grid as a means of identifying locations of bird records. The National Grid reference system was introduced in Britain shortly after the Second World War. ![]()
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