Thanks all.
Wünsch - thanks I'll give that a try
TomB - I was planning to do that but the cultivation files are too large to load - so my idea was to exclude some areas I wanted to edit and then generate those smaller areas for editing in Scenery Editor - rectangles would make this easier
TomSimMuc - again thanks for the suggestion - but I couldn't find an easy way to draw precise rectangles in GE - ie I'd like to generate a large toc file with missing rectangles and then generate those rectangles for editing in Scenery Editor - ideally using as few steps / applications as possible. Hence if it could be done in the scenProc script that'd be great.