floor plan; ground plan; plane figure
Refers to a two-dimensional drawing showing the layout of a building or a geometric plane figure. In architecture, it specifically means a floor plan or ground plan.
The architect drew the floor plan of the house.
We calculated the area of a plane figure in math class.
断面図 is a cross-section drawing, cutting through a structure to show internal details, unlike the top-down view of 平面図.
Compound of 平面 (へいめん, 'flat surface, plane') and 図 (ず, 'drawing, diagram'). The reading ず is a voiced form of 図 (と) used in compounds.