Hi Caty this is not quite the correct blog but I see the thread for ME 2011.3 is closed ref the DEM file my existing file is 471,904 kb the new one is a newer date but only 115,114kb in size so it seems to me that if I replaced this file then I would lose a lot of detail from other maps, if this iscorrect and the file in that particular thread is for Mid East area is there any way to merge them.