The floor plan is actually a section drawing in which an imaginary cutting plane passed through the structrure about four feet above! The plane has to be higher enough to cut through th neccesary details. 

The purpose of the floor plan is to show the location and dimensions of the exterior and interior walls, windows, doors, major appliances, cabinets, fireplaces and other fixed features of the house. Floor plans can also include include information which would ordenarily found in other drawings (if the structure is not too complex). For example, the electrical plan, or plumbing plan.