Methodology & Background Data
This report relies on the best available data and uses very straightforward methods to make its calculations. Sources of data can be found in the notes accompanying the Summary Data Table . The methods used to calculate measurements from these data are explained below and the actual calculations can be found in All Tables With Calculation Methodology .
High Quality Farmland
This combines the categories of Prime Farmland, Unique Farmland and Farmland of Statewide Importance, as defined by the land classification system of the Farmland Mapping & Monitoring Program of the state Department of Conservation. 
Efficiency of Urban Development
This is calculated by dividing the urban population of the county, as reported by the U.S. Bureau of Census, by the acreage of Urban & Built Up Land, as reported by the Farmland Mapping & Monitoring Program, thus producing a people per urban acre measurement. Because it does not account for urban infill and changes in the size of households over time, it probably underestimates the efficiency of new development at the urban edge. The disparity of the two data sources probably introduces some error into this measurement. But because the margin of error is replicated across all counties, we believe it to be a reliable way of comparing their relative performance. Our findings are also comparable to those in other studies measuring development efficiency in California.
Land Needed to Accommodate 2020 Population
This is calculated by multiplying the projected population in 2020, as forecast by the state Department of Finance, by the development efficiency ratio (above) in people per urban acre for the period 1990-2000. Including the entire projected population in the initial calculation, rather than just the urban component, produces a conservative result when it is compared with the amount of land currently within city spheres of influence as a measure of how much more land is planned for growth than is likely to be needed.
Projected Increase in Urbanized Land
This is calculated by multiplying the projected increase in the urban population to 2040, as forecast by the state Department of Finance, by the current (1990-2000) development efficiency ratio (people per urban acre).
Projected Increase in Rural Ranchette Development
The detailed methodology is explained in the Land Use Projections spreadsheet in All Tables With Calculation Methodology . It relies on the best estimate of the current non-farm rural population and the current average size of ranchettes in each county. The most significant (and conservative) assumption in this calculation is that only half of the new ranchettes developed will be located on the Valley floor where they are likely to affect agriculture, as opposed to in the foothills. This assumption is based on a Farmland Mapping & Monitoring Program map of Stanislaus, Merced, Madera and Fresno Counties, which is the best evidence available of the location of existing ranchettes.
Projected Loss of Agricultural Production
The detailed methodology is explained in the Agricultural Projections spreadsheet in All Tables With Calculation Methodology . It relies on average per acre market value of agricultural production on cropland and rangeland, adjusted for inflation, and the amount of each type of land projected to be lost to urban and rural development.
Development Efficiency Curves for Tipping Point Analysis
Please see Tipping Point tab in All Tables With Calculation Methodology .
 The USDA Natural Resources Conservation Service maintains another farmland database, the National Resources Inventory, that is useful in making larger-scale (national and statewide) comparisons. AFT has used the NRI in its Farming on the Edge series of maps showing agricultural areas of the U.S. most threatened by development.
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