Continuing from the previous post on mapping, an explanation follows for the coordinate system used on French IGN maps. l’Institut Géographique National (IGN) is charged with carrying out functions similar to the Ordnance Survey of UK.
The 1:25000 Série bleue Carte de randonnée is described here. Several coordinate systems are marked on these maps, early editions have no grid overlay but scales around the borders of the sheet, (see above) this made plotting grid references in the centre of the sheet difficult. Current editions now have a light blue 1 Km grid overprinted on the sheet, from this Grid it will be easy to identify which set of coordinates to use. The grid is the UTM WGS84 and is compatible with GPS. The coordinates are still shown around the border of the map (Below)
To obtain a grid ref, use the same procedure you would use for an OS map,
write the Easting first, followed by the Northing. ie. For the spot height 241 “La Petite Etoile, 6837 E 53856 N this gives an accuracy of 100 meters.
OS maps in the UK are grouped in larger grids designated by two letters. Similarly, UTM uses a Number & Letter grid. If you look back to the previous post to the UTM Grid picture, you will see France is covered by 6 UTM Grid squares. So now to complete the UTM Grid reference above, add the number & letter : 30U 6837 E 53856 N
Brittany falls on two UTM grids, 30U (the Northern coast) and 30T (Southern coast)
In summary, the UTM Grid is international and Google Earth can be set on the Preferences menu to show UTM coordinates, while the UK has the OS grid, the Channel Isles are not covered and so uses the UTM grid.