{"id":25,"date":"2012-01-18T18:40:31","date_gmt":"2012-01-18T18:40:31","guid":{"rendered":"http:\/\/www.haroldstreet.org.uk\/osgb\/?page_id=25"},"modified":"2012-06-18T06:28:04","modified_gmt":"2012-06-18T06:28:04","slug":"map-references","status":"publish","type":"page","link":"https:\/\/www.haroldstreet.org.uk\/osgb\/map-references\/","title":{"rendered":"Map References"},"content":{"rendered":"

A full reference which is unique across\u00a0Britain\u00a0will consist of two letters followed by (typically) six digits giving resolution to 100 metres eg (SS 599 939).\u00a0 Eight digits are needed for 10 metre resolution and 10 digits for one metre.\u00a0\u00a0 The two letters indicate the 100Km by 100Km square in which the point lies and are often omitted since this is usually unambiguous.<\/p>\n

The first letter gives the 500Km by 500Km square.\u00a0\u00a0 25 different letters (omitting I)\u00a0could be given here though only five actually map to the covered land areas: S for south west, T for south east, N for the north and\u00a0Scotland\u00a0and H for the\u00a0Shetland Islands.\u00a0 The “O” square contains a tiny area of the North Riding of Yorkshire near point OV000000, but it looked pretty inaccessible when I paid a pilgrimage there!\u00a0 See\u00a0http:\/\/www.geograph.org.uk\/article\/In-Search-of-OV0000<\/a> for a description by Peter Standing. \u00a0 The second letter gives the 100Km by 100Km square within that and is laid out with A in the\u00a0North Westcorner, Z in the South East thus:<\/p>\n

ABCDE<\/tt>
\nFGHJK<\/tt>
\nLMNOP<\/tt>
\nQRSTU<\/tt>
\nVWXYZ<\/tt><\/p><\/blockquote>\n

See\u00a0http:\/\/www.ordnancesurvey.co.uk\/oswebsite\/gi\/nationalgrid\/nghelp1.html<\/a>\u00a0\u00a0for a map of the squares and a good tutorial on references.<\/p>\n

The digits should be split into two groups – in the above example of SS 599 939 the point is 59.9 Km east and 93.9 Km north of the south west corner of square SS.<\/p>\n

The measurement of a reference is made easier by the regular grid of squares representing 1Km (or 10Km for motoring maps) on the ground and printed on every map.\u00a0 The references of those grid lines are shown on the margins of the map and, on some, at intervals across the map.\u00a0\u00a0 To determine a reference on a map with a 1Km grid:<\/p>\n