They can also be found on my website on the "Useful Links" page at http://mikesallright.com/links.htm
Market value, which is not the same as assessed value, is the agreed upon price between a fully informed, willing buyer and a fully informed, willing seller, neither party being under duress (such as divorce or relocation).
Differences between the two will vary as the market value shifts. If the market value for your area climbs on a steady basis your locality my reassess everyone (thereby increasing property tax revenue). If the market value declines steadily you may want to petition your assessor's office for a change in assessed value. Your property may also be reassessed if you do home improvements which require a permit.