By law, every two years the Department is required to “equalize” property tax assessments for all property classes in all assessing jurisdictions. Equalization is accomplished by increasing or decreasing the aggregate valuations of certain classes of property within each assessing jurisdiction. Equalization helps ensure that that all classes of property have been assessed at the value according to state law and that taxation is applied equitably statewide. An equitable assessment level among counties is also necessary to ensure fair distribution of school aid and other state services. There are assessors in 99 counties and in eight cities, for a total of 107 assessing jurisdictions. The Department equalizes the following classes of property: agricultural, residential, and commercial.