Architecture is the art of designing buildings. Architectural models are used by architects for a range of purposes. Ad hoc models are sometimes made to study the interaction of volumes, or to get an idea of how they look from different angles and to explore ideas. They can be used to exhibit and sell a design to help visualise a design. A model may be useful in explaining a complicated or unusual design to the building team, or as a focus for discussion between the design teams such as architects, engineers and town planners. Models are also used as show pieces, for instance as a feature in the reception of a building, or as part of a museum exhibition such as scale replicas of historical buildings.