For instance an area in california that doesn't have a lot of recent home sales will stick out as having really low property taxes, which is not reflective of the tax rate you would pay when you buy in that area.
In addition, going from price and rent to cap rate is already relatively complicated, as expenses (such as property management, homeowners' insurance, repairs, ...) have a sub-linear dependence on price or rent. This sub-linear dependence is included in the map. Using a fixed-percent model for these expenses will artificially inflate C-class cap rates, while artificially deflating A-class cap rates.
Planned additions:
1. Filters - To answer more complex questions
2. Landlord/Tenant-Friendly States (also fiscal solvency of states ... to estimate risk of property taxes rising rapidly)
[edit: formatting]
