Combining different coordinate systems

Discussion created by tom.finch on May 23, 2013
Latest reply on May 24, 2013 by MKennedy-esristaff

I'm having some cartography issues. I started off with some raster basemaps which have "User_Defined_Lambert_Conformal_Conic" Spatial Reference. These maps were created by a colleague, who tells me that they actually use WGS84. When I import WGS84 coordinates from my GPS they all match up fine. They also match up perfectly with the ESRI basemaps. No problem.

I've now downloaded some more recent raster basemaps from IGN (the French mapping folk) which use "European_Lambert_Conformal_Conic". When I add these maps to the ESRI basemaps, they show up in the Arctic Ocean, when they should be in the South of France. They also don't match up with the original ("User_Defined") rasters or the coordinates from my GPS. Note that it doesn't make a difference in what order I add the different data.

Where am I going wrong? I assume it's a transformation issue, but don't know how to fix it. Surely if ArcMap knows that one feature uses x coordinate system and another y, then it should be able to display them correctly? I think I'm fundamentally misunderstanding how it all works anyway.

Thanks in advance

PS I'm using 10.1 Desktop