Awareness of fair and affordable housing needs in regional terms is not limited to Chapter 40B. The majority of federal housing assistance programs use percentages of Area Median Income or AMI, a figure based on median household income in metropolitan and non-metropolitan areas, as the basis for setting housing program income limits. The use of an area median accounts for differences in wealth 3 CHAPTER 40B HANDBOOK FOR ZONING BOARDS OF APPEAL Chapter 1. Intrroduction between cities and towns and recognizes that housing prices have an impact on the choices available to homeowners and renters about where they will live in relation to jobs, services, schools, and so on. In Massachusetts, housing units eligible for the Chapter 40B Subsidized Housing Inventory (SHI) must be affordable to households with incomes not exceeding 80 percent of AMI for the HUD region in which the units will be located. For example, SHI Eligible units in the metropolitan Boston area, which includes all Boston neighborhoods as well as many other communities around Boston, must be affordable to the same low- or moderate-income households – meaning the units must be sold or rented in the same price range – regardless of whether the units are in affluent or working-class communities. This promotes housing choice for low- or moderate-income households within the region.