Real estate appraisal, property valuation or land valuation is the process of developing an opinion of value for real property (usually market value). Real estate transactions often require appraisals because they occur infrequently and every property is unique (especially their condition, a key factor in valuation), unlike corporate stocks, which are traded daily and are identical (thus a centralized Walrasian auction like a stock exchange is unrealistic). The location also plays a key role in valuation. However, since property cannot change location, it is often the upgrades or improvements to the home that can change its value. Appraisal reports form the basis for mortgage loans, settling estates and divorces, taxation, and so on. Sometimes an appraisal report is used to establish a sale price for a property.