There could be a number of reasons. To establish market value, the Assessor's Office gathers information from a number of sources, including previous sales from the area, zoning, topography, view, livable square footage, lot size and other component information, just to name a few. The valuation is determined by a computer analysis of the information gathered. Although properties may look alike on the surface there may be subtle differences. In mass appraisal those are not always obvious, even though they result in different values. Keep in mind the Assessor's Office must value nearly 1.7 million properties, and you have a right to appeal the value within 60 days of the date the Assessor mailed your Notice of Value, if you disagree with the value.