Real estate appraisal, property valuation or land valuation is the practice of developing an opinion of the value of real property, usually its Market Value. The need for appraisals arises from the heterogenous nature of property as an investment class: no two properties are identical, and all properties differ from each other in their location - which is the most important determinant of their value. So there cannot exist a centralised Walrasian auction setting for the trading of property assets, as there exists for trade in corporate stock. The absence of a market-based pricing mechanism determines the need for an expert appraisal/valuation of real estate/property.