Usage documentation is at en:Template:Gbmappingsmall.
Finding grid references
Good sites that are based on grid references are:
- Getamap - the Ordnance Survey's own site - combined map browse and name search
- Streetmap - furthest out zoom of map browsing
- Streetmap - name search
- Geograph - map browse
- Geograph - name and other searches
The name searches for Getamap and Streetmap are both "old fashioned" - very unforgiving of spelling and other errors. But any self-respecting Wikipedian should be able to use the zoom-in features of all three sites!
Getamap. At the limit of zoom in, clicking on the map has the effect of re-centering. Then the "grid reference at centre" is shown below the map. It can be copy&pasted direct into this template. A "six figure" grid ref such as NZ 110 642 is 100 metre precision which is usually ample for a Wikipedia article.
Streetmap. When you have found the point of interest, click "move arrow" (bottom right) then click the map on that point. On the re-loaded page, "click here to convert coordinates" (bottom). This will load a new tab. The "LR" value, eg. NS068291 is what you need. For readability spaces can be added, eg. NS 068 291.
Geograph offers the bonus of finding images licensed for use in articles. NB. if you are uploading images, please, please, please use Magnus' tool to upload them to the Commons. This will do several clever things, not least being to save you copying the image to your machine. Commons images may be used exactly as though they had been uploaded here - you do not put Commons in the link. Eg. for this photo by Tam of a man in a tam, you would code [[Faidhle:Donald Dewar wrapped up for the cold 1646273.jpg|thumb|Caption]].
Aside on postcodes
Post codes are for cab drivers with sat nav not for Wikipedians. The example I always cite is the summit of Beinn Nibheis. Sure, Streetmap will give you a postcode: PH33 6SY. But if you pump that back into Streetmap it will go to a point almost 4 km away.