thumb|right|370px|[[Amiens Cathedral floorplan: massive piers support the west end towers; transepts are abbreviated; seven radiating chapels form the chevet reached from the ambulatory]]
In Western ecclesiastical architecture, a cathedral diagram is a floor plan showing the sections of walls and piers, giving an idea of the profiles of their columns and ribbing. Light double lines in perimeter walls indicate glazed windows. Dashed lines show the ribs of the vaulting overhead. By convention, ecclesiastical floor plans are shown map-fashion, with north to the top and the liturgical east end to the right.
Many abbey churches have floor plans that are comparable to cathedrals, though sometimes with more emphasis on the sanctuary and choir spaces that are reserved for the religious community. Smaller churches are similarly planned, with simplifications.
Design
Cathedral floor plans are designed to provide for the liturgical rites of the church. Before the legalization of Christianity by Emperor Constantine, Christians worshiped in private homes or in secretive locations. Once legally able to publicly worship, the local congregations adapted the available Roman designs to their needs. Unlike the Roman and Greek religions, where priests performed rituals without public participation, Christian worship involved the believers. Thus, the limited spaces typically used in pagan temples were not suitable to Christian worship.
- Ambulatory: A specific name for the curved aisle around the choir
- Crypt: Usually the below ground foundation. Used for burial or as a chapel.