Hi Gerd, cgpsmapper can create 3 types of map: - transparent - TRE flag set and no background - semi-transparent - TRE flag not set and no background - normal - TRE flag not set and background exist For normal maps, cgpsmapper creates background rectangle if no background object exist in source code. Background object is defined by explicit declaration "Background=Y". I'm not sure if this declaration could be added to any other object type than 0x4B. Probably marine maps use other type for background. I think current algorithm in mkgmap is good enough. What you can add is an option to stop creating default background, like for example --background=no. But I don't think it would have much use. I don't know if there is any peculiarity to background object in img. Is it marked as background somewhere in img data? If yes, then you can consider adding an ability in style to set this marking, for example like "set mkgmap:background=yes". -- Best regards, Andrzej