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Ordnance Survey FAQ and Excel Mapping Routines

How do I set my GPS receiver?


If contemplating use of a global positioning system (GPS) receiver in Britain it is essential that the OS format is catered for if you wish to relate it to any paper based map.

Garmin receivers

In the case of the Garmin 38, 45, 12, 12XL, eTrex, Oregon/Dakota families (and probably all other walking devices) you should set ‘British Grid’ for format on the navigation setup page.  Datum should be set to ‘Ord Srvy GB’ to avoid errors of up to hundreds of metres.   I choose to set my GPS for metric measurements rather than statute for walking since the maps have a 1Km grid, but tend to use statute for motoring to match the odometer in the car and the road signs, both of which use miles here in the UK!   ‘Auto magnetic’ for north gives good results and complements my trusty Silva compass, and that was how I set my GPS when I first used it.   More recently though I have found it much more convenient to set the GPS to ‘Grid’ and I then have consistency between GPS, map and the protractor scale on the compass using the method above.

The OS reference is given by a Garmin with a resolution of one metre (but not to that accuracy!) – eg.

SJ  12345
BNG 67890

This example shows we are in the 100Km square SJ some 12345 metres east of the square origin and 67890 metres north.  The BNG refers (presumably) to British National Grid.   When inputting the grid reference of a waypoint, note that the receiver requires the two letters and five digits of eastings on one line, and five digits of northings on a separate line.

Magellan Blazer 12

Paul Slootweg has kindly sent information on the Blazer 12 GPS system:

“This GPS received includes support for the OSGB grid system.  To configure, simply use the ‘menu’ button and select the ‘Setup’ menu.
It will then offer the option to select ‘COORD SYS’ (coordinate system) and choose the OSGB option.  Then select the ‘MAP DATUM’ and
choose GRB36 (OSGB)

If you pick OSGB it won’t allow any other datum than GRB36, which avoids the possibility of positional errors. It imposes similar restrictions with
some of the other grid systems to ensure the positional data is correct.  The unit also allows the selection of magnetic or true north.

The display will show OS references

 SJ 1234 

consisting of 2 letters and 2 groups of 4 digits – i.e. 10m resolution,
which seems more than enough for my use.”

Paul believes that the same settings will apply to other Magellan systems.

Phil Brady © 2020