Google earth is good but it is not perfect (something for the future development perhaps), it doesn't allow you specify a local datum. It doesn't even specify the datum it uses but I suspect as the software is being designed with GPS in mind then the datum will most likely be the default one for most GPSs. WGS-84

Firstly you have to convert the OSGB36 coordinates into WGS84, you can do it here at


It even gives a script for the spatial transformation from the OSGB36 to WGS84 if anyone is interested.

When you plug in the coordinates NO369741 you get Lat 56?51′17″N and Lon 003?02′02″W

As google earth uses North (latitude) East (longitude) notation by default you would have to specify these as the conversion gives a North (latitude), West (longitude).

For the Google Earth this can be done if you enter N 56 51 17/W 3 02 02

or 56 51 17/-3 02 02 in the standard google earth notation.

This again could cause some problems if the notation isn't specified i.e. N(lat) E(lon) or N(lat) W(lon) as well as the different formats such as DDD, DMS or DMM etc

Or you could just plug in the OSGB map reference into the ordnance survey maps website at


just plug in NO369741 where it says 'place name or postcode' then hit go. The accuracy is 100m by 100 m. To specify a more accurate map reference you would just make the coordinate an 8 or 10 digit number. Such as

NO36917415 - accurate to 10 metres
NO3691274156 - accurate to 1 metre

distances between grid references are easy to calculate, just use Pythagoras Theorem.

Example Calculate the distance between NO369741 and NO243861

Distance = Sqrt((243-369)^2+(741-861)^2)*100 = 17,400 metres away!! Anyone want to calculate the grid bearing and the magnetic bearing from NO369741 smile

Edited by bentirran (06/30/07 09:59 PM)