[arnsholt]

In this context, it's not terribly hard to divine that they probably mean EPSG:4326 coordinates. I was going to comment that one of the ETRS89 UTM zones might be easier to work with, but on second thought the data almost certainly includes the DOMs if not the TOMs, so a global coordinate system is probably best.

[manarth]

The BAN provide fields `long` and `lat` which are WGS84, and also `x` and `y` which are coordinates expressed in "the appropriate local CRS" (without much elaboration on what that would be).

[willyt]

That would be the French national grid system, no? The UK has the ordnance survey grid which is based on the OSGB36 datum. I'm pretty sure France will have a similar national datum to create their own local grid coordinates as planning and building works needs to be done in a more accurately aligned local datum than WGS84.

[wongarsu]

For mainland France it's reasonable to assume the French national grid. But what about French Guiana in South America or Mayotte in Southern Africa (an island north of Madagascar)?

France still spans the globe, with many places treated as equals to the French mainland.

[ryandrake]

Not to mention that “latitude” and “longitude” cannot uniquely describe an address, regardless of the datum or ellipsoid. Maybe that is not the intent of storing the coordinates. Lat/Lon says nothing about floor number in a multi-story apartment.