Bonne to KML & KMZ

Good to know

• Datum: Treated as WGS 84, no shift (the datums agree to about a metre or better).

Convert a whole spreadsheet

1. Open the web app or the Windows app, and paste your rows from Excel or open a CSV file.
2. Under Coordinate system, search for “53024” and pick Bonne.
3. Check one point you know on the map, then press Save KML or Save KMZ and open it in Google Earth.

Common mistakes with Bonne

• Feet entered as metres. Bonne is in metres. Coordinates copied from a drawing in feet must be converted first, or every point moves outwards from the grid's origin.
• Forgetting the datum. Bonne is not on WGS 84: treated as WGS 84, no shift (the datums agree to about a metre or better). Picking a WGS 84 grid with the same projection instead leaves the points off by that amount.
• Points outside the grid's area. Bonne is meant for World. Points well outside that area convert with growing error; the converter flags them so you can choose the right grid.
• A local site grid. If every point is off by the same distance and direction, the drawing may be on a local site grid. Calibrate on three or more known control points instead.

New to this? Read how to convert easting and northing to latitude and longitude.