The focus of this research paper is the use of geographic information systems (GIS) for situs analysis as part of the valuation of a major retail redevelopment. This analysis was done as part of the research for the proposed redevelopment of a retail site with known groundwater contamination issues resulting from its prior use as a regional mall. The Royal Institute of Chartered Surveyors recognized the importance of the concept of the spatial analysis of locational attributes in their RICS Practice Qualifications (2002). It refers to the process as Geomatics, which is listed as a core competency in their educational requirements. Appraisal organizations elsewhere have not done so. The research paper uses GIS for in analyzing the rates of absorption of new shopping centers in the Los Angeles Basin vs. access, competition, trade area demographics, and resultant values. If the technique had been part of conventional appraisal practice, it could have warned the developers of major retail centers of the major financial problems that subsequently occurred. The research paper recommends including GIS, fundamental market analysis, and situs analysis as international Best Practice techniques for real estate appraisal. It is an opportune time to identify the Best Practices for valuation that are most likely to lead to the most accurate appraisals for the newly emerging international valuation standards.