I was creating a new map just now, and while I should have realised that it would probably not work in its current form, the error message caused al lot of confusion and initially led me down the wrong track. C:\Program Files .\therion.exe: error -- INDEXGLMESM_System.th [134] -- incompatible map projection -- SwissM_PlanMap@GLMESM_system I started looking through map definitions to find which one was not defined properly as a plan, despite knowing they all must be, as they have worked for years. map GreenlinkAreaPlanMap -title "Greenlink Area<br>Plan view" -projection plan # overview map focusing on surface features preview below SwissM_PlanMap@GLMESM_system preview below DwarfsDoorPlanMap@GLMESM_system preview below MiddleEarthPlanMap@GLMESM_system preview below GreenlinkPlanMap@GLMESM_system preview below BlackSabbathPlanMap@GLMESM_system endmap GreenlinkAreaPlanMap The problem turns out to be that a map definition must contain more than just previews. If I remove 'preview below' from one of the definition lines, all is well. I suggest that the error would be more helpfully be reported by Therion as; "map must contain at least one scrap, survey or map without preview" Bruce