The land inventory is based on several sources. The polygon geography is taken from appraisal district parcel layers merged together. A land use inventory is performed by classifying land according to a coding system that reflects the primary improvements (buildings or structures) on each parcel. Most of the land use information is attached through a GIS Union from past land use inventories. Undeveloped parcels are checked against building permit, aerial photos, and appraisal records, generally collected during the fall, or when data was made available. Information is collected only in the City of Austin’s Full, Limited Purpose, and Extra-territorial jurisdictions, and not entire counties.