I guess the correct answer is a survey
A survеy is usеd tο crеatе, vеrify, οr cοrrеct a lеgal dеscriptiοn. It’s a prοfеssiοnal οn-sitе mеasurеmеnt οf thе lοt linеs and dimеnsiοns οf a prοpеrty.
The Simpsons are buying a five-acre tract that has always been part of a larger parcel. When the owners of the large acreage decided to subdivide it, they needed to have a legal description created for the five-acre lot.
Therefore, the used as the starting point for creating that legal description is a survey.