Ok, Now I feel like a beginner, having to ask this question. I have for years created my .th files like this, more or less. input 1-BottomUpPlan.th2 map 1-BottomUpPlanCL -title "1-BottomUp plan centreline" -projection plan 1 # this works fine endmap map 1-BottomUpPlan -title "1-BottomUp plan" -projection plan 1-BottomUpPlan-s1 endmap survey 1 -title "1-BottomUp" centreline etc endcentreline endsurvey This is contrary to the current good advice, and the way TopParser works, which suggests that maps should be created inside the survey, as this makes referencing the scraps easier and more consistent when they are part of a large project. So with this brand new project, I rearranged my 1-BottomUp.th file like this, to try to follow good practice . survey 1 -title "1-BottomUp" input 1-BottomUpPlan.th2 map 1-BottomUpPlanCL -title "1-BottomUp plan centreline" -projection plan 1 # this always causes error at this location "object does not exist - 1" endmap map 1-BottomUpPlan -title "1-BottomUp plan" -projection plan 1-BottomUpPlan-s1 endmap centreline etc endcentreline endsurvey Trouble is, the Therion Compiler always reports an error "object does not exist - 1" when I try to create a small map with just the centreline of survey 1. I have tried a number of variations of the above, with versions from 5.3.16 to 5.4.1, and the only way I can get it to compile is with the arrangement at the top of this post; how I have always done it for years and years. So it looks like Therion is complaining about calling the survey "1" from within the definition of survey "1". I would not have thought this were a problem, as it seems like Therion is generally happy to do this sort of thing. Is it some kind of namespace problem? Or is there some other thing I am missing? Is it not possible to create a map of containing only a survey centreline, from within that same survey? Bruce