If you have a paper Ordnance Survey (OS) map, GridPoint GB makes it easy to locate yourself — even when you've got no mobile reception.
GridPoint GB uses your iPhone's GPS and compass to provide your current grid reference and heading, and illustrates how to use this to locate yourself on the map. Coordinate conversions are implemented via OS's OSTN02, and are thus accurate to within 1m.
New in version 2, the app also:
* Reports full numerical easting and northing, tetrad, and raw latitude/longitude, and various heading parameters
* Has a sharing facility so you can share, copy or store your location
* Calculates next sunset and sunrise times
* Can emit a distress signal, just in case
For details and instructions, please see http://mackerron.com/gridpointgb/
Please note: this app works ONLY in Britain (i.e. England, Scotland or Wales). It does not operate in other parts of the UK or British Isles and cannot provide coordinates in Northern Ireland or the Republic of Ireland, since a different coordinate system is used.