Drawing the Lambert grid

To draw the Lambert grid

• Work on a large, clean, flat table, cleared of all things.
• Unfold the 1:25,000 map
• Use a sharpened black pencil (never use ink)
• Use a 12" ruler. (at least)
• Look for the small crosses that are drawn every cm on the map.
• Link these crosses to form a nice regular grid.
• Extend the lines to the sides of the map. Only the digits that are in the alignment are interesting. Do not bother to use the other digits. If the grid looks tilted on one side or the other don’t worry, it’s perfectly normal.
• You’re done !

The Lambert coordinates

Each square in the grid is 1 km long. To define a new set of coordinates all you need to do is define a new reference.

e.g. on a 1:25,000 map :

coordonnées d’un point

The coordinates of point A are :

Point A : X = 442,725 and Y = 1 123,375

You need to be very precise ( 1mm = 25m on the field)