There are factual errors on your property assessment data card.
The first item is the easiest to correct if there are errors on your assessment card. Your best course of action is to obtain a copy of your property tax card (available at your city or town hall) and look at the information on the card for accuracy. You will find a “footprint” of your residence. Check to see if the measurements are correct. Are porches taxed as living area? Is the deck that you tore off or the shed you disposed of still being listed as a taxable item?
For tax assessment purposes second floors of residences are classified as either full story (equal to the living area below), half story (half of the living area below), and three quarter story. These second floor measurements (1.00, .0.75, or 0.5 of the first floor) are based on an eyeball view of the second floor. Some older style capes have half the living area of the first floor and capes with full dormers have ¾ of the first floor. Colonial or two story residences will have a second floor equal to the area under.
The two most common disparities in assessment records are either exterior measurement errors or basement finishes. In some cases a basement was finished and not picked up by the municipality. Or, if there was an error in the initial measurement of the residence it can carry forward for years.
Pointing out an area of data that is incorrect is the easiest of the three methods; it can also have an unintended effect. In order for a municipality to understand where their error is located, they will require access to the residence. So if you intend to show the tax assessor that your three season porch is not heated or you have two bathrooms, and not three, the assessor may also view that the basement is now finished and the kitchen was remodeled. Consider the pros and cons of this approach when seeking a tax abatement.