A complex is a set of two or more structures belonging to a single plan. This organization is designed to group the pages of related buildings together, and to simplify the organization of company portfolios.

Normally the different buildings in a complex are built by the same developer, or at least by a succession of developers working on a common development outline. In some cases a complex may be spread over a city or split into different geographical units, and they may also cross city borders if the different parts are adjacent to each other.

Examples of complexes include:
a) groups of structures that form a single development (office, residential, etc.);
b) a school or university, either on a single campus or split between multiple sites within a city;
c) mixed-use complexes of more than one tower built according to a single development plan;
d) a hospital complex under one management. (A medical center made of several different hospitals would normally be classified as a zone.)

Buildings can be incorporated into complexes after their completion, if they are purchased or leased for use by certain complex types such as universities or medical centers. If a building is only partly occupied by an institution (e.g. a university) which forms the basis for a complex, then it is not included in that complex unless it is entirely owned or managed by that institution.

A company can be connected to a complex if it performs the same role with regard to each structure in the complex (for example, the owner is connected only if it owns each building); otherwise the company will be connected to individual buildings. Whenever a company is connected to a complex it shows up on each building page; in these cases the company's association with the displayed building can be assumed.