The assessment is the total value of the land and all permanently attached structures (buildings, trees, landscaping, etc.). It also is just the value used for taxing purposes, it does not necessarily have anything to do with the fair market value, as long as similar properties have a similar value.
For the value of your land (when calculating depreciation for business or rental property) you want to know what the empty lot would sell for if the house or building was demolished. The assessor might be able to help, or you might need to ask a real estate professional.
