cross-section view; sectional view
Technical term used in engineering, architecture, and design to show the internal structure of an object as if cut through.
Looking at this cross-section view, you can clearly see the internal structure of the building.
The designer explained the pipe locations using a sectional view.
立面図 is an elevation view (side view), while 断面図 shows the interior after a cut.
Compound of 断面 (cross-section) + 図 (diagram). The reading is standard on'yomi.