Thank you for your comments, Mark. Here's the latest one which I think will meet what you have in mind:
It fits into a space 8ft by 8ft (in the photo, the purple plastic box on the right is 8ft from the left hand skirting board and the road from the level crossing out of the layout just crosses a line 8ft from the further skirting board. On display the left hand side with the through track would be at the front.
I've "populated" the interior of the layout with one or two ideas - the bus station/taxi rank (I do have the airport bus station and so with that and the sign to the bus set to "Airport" the railway can be linked to the airport display. I thought there might also be room for a small shop/cafe in that area (I've an old, small, early System-X building which might form a basis for it) plus other buildings. The warehouse could be supplemented by a forklift and truck being loaded and with some drums and maybe a van parked behind it.
The fire station I'm thinking of is a 3/4 bay custom with an old Steck practice tower and not the big 4819 set which may take up too much room. (I've never got round to building it yet so I don't know how much room it takes up exactly), and that might usefully sit just outside the layout handy for fires in the station area or the town.
I must admit that a "square" layout strikes me as unusual, but if it works then it works.
