Georeferencing to an Unknown Coordinate System

Discussion created by Sean.McDade on Jan 12, 2012
Latest reply on Jan 24, 2012 by sebastian_4m

I'm currently trying to georeference an old map (1955) however, I can't find the map's coordinate system in ArcGIS 9.3. The info I have is as follows

Projection: Lambert
Ellipsoid: Clarke
Equal Distance of line: 100 metres

It appears to be a Lambert equidistance projection but none of the projections in ArcGIS 9.3 have a Clarke ellipsoid. I have tried the various equidistant projections in ArcGIS 9.3 and even tried modifying the ellipsoid to Clarke but have had no luck. Can anyone help by pointing me in the right direction.