[Therion] Overlaying xvi file and map background as the same scale

Hi, I want “Therionise” a cave map wich is alredy drawn. I have the data survey but not the vector data. - I created a centerline - I digitalized the map. - I import it and the xvi file in my .th2 as backgrounds. The problem is that scale of xvi file and map image are not the same. How can I overlay them at the same scale? Thank’s and sorry for my bad English, Martin