How can my assessment change when I haven't done anything to my property?

Since assessments must be set at market value, rising real estate values in the City resulted in higher assessments. As property values change in the marketplace (sales), those changes must be reflected in the the assessments. All properties, however, do not change in value to exactly the same degree. Many factors influence values. Among the numerous factors to be considered are location, condition, size, quality, number of baths, finished basement, garages, and additions.