Layouts for model railways are of two general types. The older type which is still used extensively has the layout fixed in place, such as being attached to one or more walls. Layouts of this type are often called static. Our club's main layout, the Waitemata and Chelsea Railroad, is of this type. The newer type of layout is made up of sections called modules. The modules are build to a set standard which ensures modules can be joined together to form a medium-sized or large layout. This type of layout is called modular.
The key point about modules is that, unlike static layouts, they are portable. They can be transported in cars and vans to a new venue such as an exhibition or train show, assembed to form the required layout, used, and then dissembled and move to their next location or put in storage.
A common size for a module is 1200 mm long by 600 mm wide. This small size along with the need to ensure the tracks of neighbouring modules meet exactly might suggest the modules in a layout are similar in appearance. This is far from so. Modules can have differing terrain and structures, different numbers of sidings and spurs, and different amounts of urban and rural aspects.
Some modular layouts are point to point. Others are continuous. This latter type requires special modules for the corners. These too must be built to a standard.
The club has an HO modular layout that consists of four corner modules and over 20 straight modules. Many of these modules were built by club members at home, and are stored at home. Some members have built more than one module. Any member can build a module. The document that specifies the standard for these modules is available here.