Tax assessments are just that, assessments of value done by someone who has probably never seen the home and is going by average increases or decreases of homes sold in the area. The do not take into account updates that may have improved your homes value or conversely the updates the homes that sold had done that improved the value of those homes but not yours.
Remember this is the value estimated on July 1st 2012 so it is already 6 months behind so the actual value may have gone up or down since then.
You can appeal this assessment, but do it fast as you are only allowed a few days after the assessment in issued.
These are really just an estimate of your homes value and do not in reality have any effect on the sale value of you home the only true test is by selling the home, the price a buyer is the only true value you can assign to your home, soon to be theirs!