When the assessor has determined and recorded the value of the land exclusive of improvements on each lot in his district, or in a section of his district, he will proceed to determine the value of the improvements. To secure uniform assessment of buildings and other improvements, it is necessary to establish what may be called factors of value. Architects and builders generally estimate the cost of a building by its cost per cubic foot of contents, counting from the bottom of the excavation to the top of the building. This system is impracticable for assessors because it is too complicated and requires information not readily ascertained. It is impracticable for the assessor to obtain the height of all buildings, to say nothing of finding out how deep they are below the sidewalk.