Good question! Keep this in mind: what your property is worth and what the tax office appraises are two completely different things! Unfortunately, they don't necessarily have anything to do with one another. You should also note that any given property has at least three different and legitimate values that can be assigned to it; two of which are the valueation for tax purposes and the value for marketing purposes.
In other words, you should only worry about what they appraise your property for if it seems to be too HIGH; then they could be charging more tax than they should! If it's too low, that will not affect it's actual market value or what it's "worth" or the actual so called "property value." It's only a basis for taxation that only has foundation in their world, not yours.