Hello Christiaan and David
That's really helped - thank you!
Am probably going to keep using classes for seats, sightlines, building, staging, technical etc. then separate design layers for each seating layout. Have tried that the last couple of days and it seems to work.
Christiaan - when I said "An alternative would be to do it on one sheet layer, and copy the building etc. over." I meant to draw the rooms walls etc, group them and then copy them into a different place on the same design layer - once for each different seating layout. I would then draw the different layouts on each of the copies (hope that makes sense !) and set up different viewports on separate sheet layers. But I think I will forget that method now anyway !
Also - that's a great tip Christiaan - to double click the viewport to edit the design layer that way - I hadn't seen that option.
One thing that really confused me was how a symbol can be assigned a class, (for example "chair") when inserting it into a drawing - but it can also have a class definition embedded within the symbol ("seat" for example). This caused me a lot of confusion, as I was assigning the class "chair" to a chair, then wondering why I couldn't edit it when my active class was "chair". I then realised that when I edited the symbol, it was assigned the class "seat" within the symbol definition. Do many people get caught out like that or is it just me ! (at least I now know)
Many thanks again,
Andrew
PS - David - as we work in a similar field, can I ask - do you draw in 3d in Vectorworks ??