we starting the On30 modular layout after the building a OO ones for Cheshire Railway Modellers
http://www.cheshirerailwaymodellers.org/
we adopt a standard depth of four inches between track and table top This would allow low road or river bridges within the confines of the modules, or even just tracks running in embankments for evocative low angle photos.
A four inch long inter-module bridge sections is used to join the modules togetter
Scenics do not have to match on any of the modules as there is a gap between each one
When we set up the layout we can use table to sit the modules on with 1 module that drop below the table as as Forks Trestle dose resting on 2 tables