Streetmap funny

From Rhaworth

There is a facility, coor_g.php, mainly used by Wikipedia, which takes an OS grid reference, converts it to latitude and longitude and links to a map sources page, thus: TL 473 132. offers a facility to display the current location in a number of coordinate systems thus.

There are noticeable differences between coor_g's idea of gridref → lat/log conversion and streetmap's as can be seen by clicking on the links in the table below. In the worst case (top left of the table = north west) there is a difference of 39 metres in longitude. (The latitude figures show reasonable agreement throughout.) That example is all at sea - the worst case for actual GB land is Soay, St Kilda where the difference is 24 metres.

Who is right coor_g or streetmap?

0 100 km 400 km 700 km ← eastings
0,1300 100,1300 400,1300 700,1300 1300 km north
0,800 100,800 400,800 700,800 800 km north
0,400 100,400 400,400 700,400 400 km north
0,0 100,0 400,0 700,0 0 north
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