The attached link is a column from the North Shore News that simplifies the confusion

In a nutshell, the assessment office looks at the same things we as Realtors do.  The size and condition of the house, size of lot, view or no view, and if the property is on a main road.  The assessment office use Google Street View, high quality aeriak photography from municipalities, as well as they keep tabs on building permits, rezoning regulations and official community plans and MLS listings for interior views.

more info and how to appeal can be found below