Not sure exactly what you are asking. On a residential property the value of the house is assessed and the value of the the land is assessed. This value, the county's assessment, can be higher, or lower, than the "market" value of a home. Taxes are computed on the county's assessment of value for the home.
Assessed value is the dollar value assigned to a property for purposes of measuring applicable taxes. Assessed valuation is used to determine the value of a residence for tax purposes and takes comparable home sales and inspections into consideration. It is the price placed on a home by the corresponding government municipality to calculate property taxes. In general, this value tends to be lower than the appraisal fair market value of a property.
Assessed value is an approximation of what the home may be worth for the purpose of taxation. Some people get confused with assessments and appraisals. Appraisals are much more detailed and accurate. The assessed value of a home will have little relationship to its actual value when you buy or sell. It may be worth more or less than the tax assessment.
Once you purchase the home you may find that the assessment will change to reflect what you purchased it for. This varies in different areas, but if it does get reassessed for your purchase price, this may be the only time it is accurate.