1911 Encyclopædia Britannica/Plan

PLAN (from Lat. planus, flat), a diagram on a flat surface; hence by analogy any deliberate scheme or design. In architecture, a “plan” is a horizontal geometrical section of the walls of a building, or indications, on a horizontal plane, of the relative positions of the walls and partitions, with the various openings, such as windows and doors, recesses and projections, chimneys and chimney-breasts, columns, pilasters, &c. This term is sometimes incorrectly used in the sense of design (q.v.).