Compilation is based upon a classification scheme identified in the Appendix .
Acquisition Processing Steps Manual interpretation of aerial photographs acquired from NASA high-altitude missions and other sources were first used to compile the land use land cover maps. Secondary sources from earlier land use maps and field surveys were also incorporated into the LULC maps as needed. At a later time, the LULC maps were digitized to create a national digital LULC database. Initial source preparation involves the transfer of field survey information, photo classification detail and associated line work to a base map for digitization . This may be done through stereo compilation or monoscopic transfer techniques.