planform

Planform, or plan form, is the term used to describe the top-down projection or layout of a design. It is the geometric shape seen when looking down on a wing, hull, building, or urban site, and it is a primary factor in performance, stability, and circulation. The planform concept applies across engineering and design disciplines, and the choice of planform shapes influences how a design behaves and functions in real use.

In aircraft design, the planform defines the wing shape as seen from above. Common planforms include rectangular, tapered, trapezoidal, swept, and delta shapes. Key parameters are sweep angle, taper ratio, aspect ratio, and root and tip chords. The planform affects lift distribution, induced drag, stall characteristics, and structural weight. Generally, higher aspect ratio wings with gentle taper reduce induced drag, while swept or delta planforms enhance high-speed performance but can increase pitching moments and wing loads.

In naval architecture, hull planform refers to the shape of the hull projected onto the horizontal plane. Planform considerations influence resistance, stability, maneuverability, and seakeeping. Elements such as midship sections, flare, and beam distribution affect performance in waves, turning radius, and loading.

In architecture and urban planning, planform describes the layout of built form and spaces as seen from above, including blocks, streets, courtyards, and room arrangements. Planform decisions impact circulation, daylight access, land use efficiency, and visual coherence.

Planform is typically quantified by the projection area and related metrics, such as aspect ratio in wings (span squared divided by planform area). The term emphasizes the importance of top-down geometry in design and performance.