How is the "Assessed Value" calculated

[Eric Hathway]

I have bought some properties above assessed value and some below. Assessed Value and market value don't seem to be parrallel. Can someone explain the difference?

I mostly interested in multi family buildings. A lender brought it up to me that the assessed value is low compared to the agreed purchase price and she wasn't sure it would appraise. Going by cap rate and the area's gross income multiplier, my deal is great...