use GIS and spatial data for local planning. Community 20/20 software was designed to enhance access to geographic information, to put HUD in the forefront of using spatially enabled technology, and to facilitate local planning processes and community efforts to prepare their consolidated plans (Box 2.2). HUD’s follow-up program, Enterprise GIS, continues this effort (Box 2.5).

Informal settlements along the U.S.–Mexico border (colonias) are a good example of the need for understanding local conditions, for attention to processes at work at the regional level, and for putting relevant geographic information in the hands of local decision makers. HUD could use GIS in the colonias to evaluate the question the appropriate scale for the analysis of urban problems, assess the regional labor markers, identify housing and rental prices as a determinant of colonias development, monitor transnational processes between the United States and Mexico, and analyze the changing economic practices of unregulated urban settlements (see Box 3.1). Aerial photographs make effective visual tools because customers can “see” the area in question and better understand the other data that is overlaid on the map. The partnership between HUD and the U.S. Geological Survey in the colonias has made good use of these photos (Figure 3.2).

Although visualization is a powerful tool for community groups and policy makers alike, the complexity of some urban problems requires advanced analytical techniques including statistics and modeling. Spatial analysis can inform our understanding of social problems and suggest public policy response. For example, understanding private housing markets is critical to housing voucher use. Housing vouchers work well in urban areas where there is a surplus of housing and landlords are happy to have the opportunity to rent their apartments through HUD’s voucher program. In tight housing markets, landlords have little incentive to accept housing vouchers. When demand for housing exceeds supply, prospective tenants bid up the price of rental units. In these situations, landlords often prefer to let the market work, since rising demand leads to higher rental prices. Individuals who have vouchers in these situations may find that they cannot secure a place to live. GIS could provide a framework for keeping track of trends in the private housing market including rental prices, and lead to the development of additional means to provide affordable housing in urban areas.

GIS can be used to analyze the availability and spatial distribution of housing for people with low income. Nationally, the availability of affordable housing is lower in the suburbs than in the cities. In the 1990s, housing costs