Many jurisdictions now have computerized geographic information systems that are used by many branches of government. These systems integrate ownership records with information about zoning, sewage systems, land use, soil types, communication networks, geologic structure, and a host of other data. In short, the assessor's office has an abundance of data relevant to the value of your property. Incidentally, this information makes the office an important community resource. To apply this information to valuing property, the assessor constructs a model-a simplified representation of how market factors affect value.
Most residential property is valued with a cost model or a sales comparison model.
A cost model says the estimated market value of your property equals the value of the land and the cost of constructing a replacement, less depreciation. Replacement cost is usually found by a cost manual that shows regional construction cost for all building elements. Depreciation depends largely on age, condition, and the current desirability of the property's features and location. Sales comparison models are usually more important in appeals. A sales comparison model says the estimated market value of your property equals the sale price of a comparable property, with adjustments to the sale price for differences between your property and the comparable.