I believe what you have is a notice of Property Tax Assessment;
http://thespec.com/article/436868
From the article;
MPAC insisted that an increase in assessment would not automatically translate into an increase in property taxes, which are set by local municipalities.
If the assessed value of a home has increased by the same percentage as the average in the municipality, there "might" be no increase in property taxes for that homeowner.
I know that's a pretty big (and unbelievable)
'might'.