It is no secret that California is short on housing units, but the questions of where and how much to build are rarely easy to answer. Cities and counties are charged with the responsibility of developing not only communities in which people live and work, but also with protecting the health of the surrounding natural environment and agricultural lands. To achieve balance between these core values, advocacy groups and government agencies alike have taken interest in understanding the available supply of land and the capacity for planned growth in their regions. This interest has spawned a number of recent studies on the matter, with more on the way. These reports focus on detailed descriptions of land supply and planned capacity, future demand, growth visioning, and are in many cases expressly designed to influence policy, particularly a general plan update process. While city planners often know inherently where development potential exists, inventories and monitoring put numbers to this ground knowledge, reveal hidden potential, inform the public, and provide a basis for weighing alternatives. One straightforward approach is the City of San Jose's "Vacant Land Inventory" issued in July 2002. The study uses aerial photography to identify 2,200 acres of residentially zoned land, which it disaggregates by 13 geographical regions. The study further breaks down the properties by the density of residential zoning, which includes categories such as urban hillsides, transit corridor and high density. Another example of an effective capacity study is embedded within Contra Costa County's 2001 housing element update. The study identifies vacant and underutilized land using a parcel specific land-use geographic information system. In addition to a regional breakdown of vacant acres, the study has also computed a regional breakdown for housing capacity and has evaluated the potential for affordable housing. Sacramento County has conducted a similar study in its 2002 housing element update. A report issued by Greenbelt Alliance in November 2002 titled "Vacaville At A Crossroads" is an example of a similar effort by an advocacy group. The report examines housing potential under current plans as well as the effect of several proposed city annexations, and changes in zoning codes (like creating mixed-use corridors). The report, which presents less technical data than some, focuses on sustainable development and presents an alternative to the status quo by directing future growth away from valuable habitat and farmland and into communities. While some studies focus on one city or on unincorporated county land, regional studies can provide a more comprehensive understanding of growth potential and regional choices. One such study is "Room Enough: A Report on Responsible Development in Monterey County," published in September, 2002 by Landwatch Monterey County, a non-profit group focused on promoting land use legislation. "Room Enough" is aimed at evaluating the entire county's capacity to meet its projected housing need while converting as little farmland and open space as possible. Although the predominant trend has been that cities and counties studies for only their own jurisdictions, a few councils of government (COGs) have begun processes that are regional in scope. Recognizing that growth patterns often have little regard for county lines, the Sacramento Area Council of Governments (SACOG) has initiated the Sacramento Region Blueprint, which looks at growth in Sacramento, Placer, El Dorado, Yuba, Sutter and Yolo counties. This effort to provide background support and visioning for regional growth for the next 50 years weaves together the planning fabric of many cities and counties. While a vacant land inventory or capacity study is usually informative in its own right, the choices for future growth come into perspective when compared with projected demand. San Jose looks at past rates of land absorption, from which one can make assumptions, but provides no projections for demand. The Contra Costa housing element update sets its framework by evaluating its supply against the Bay Area regional housing needs assessment, as does the Vacaville report. The "Room Enough" report uses Association of Monterey Bay Area Government population projections for 2020 to predict growth in the region. The Sacramento Region Blueprint also bases demand on modeling scenarios. One of the biggest keys to a successful study is in how it plays into the larger planning process. For instance, the Contra Costa and Sacramento housing element updates are part of general plan processes, so the studies' results feed directly into shaping the general plan. They are straightforward reports that play straightforward roles. "Room Enough" was designed to provide background data and support a smart growth approach to Monterey County's general plan update. "Vacaville At A Crossroads" is part of a campaign to influence Vacaville's visioning process and to change the city's general plan. The Greenbelt Alliance recently published similar reports, including "Contra Costa County: Smart Growth or Sprawl," which is designed to build support for smart growth and open space protection in Contra Costa County. The Sacramento Region Blueprint prepared by SACOG is much broader in scope and encompasses many aspects of the planning process, from public outreach to informing decision-makers. The San Diego Association of Governments is also embarking on a regional comprehensive plan aimed at, among other things, integrating the region's approach to land use and housing for the future. These are two examples of large-scale regional programs designed to understand effective use of a region's land supply.