Dasymetric Mapping Techniques For The San Francisco Bay Region, California
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| Example of population density using choropleth and dasymetric mapping techniques |
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The San Francisco Bay region’s population has grown from approximately 6 million inhabitants in 1990 to 6.8 million inhabitants in the year 2000 yielding a 12% growth increase. Spatial analysis of the nine-county region is necessary in order to conceptualize urban growth patterns essential for land-use planning and urban-growth modeling. Cartographic representation of human population distributions and socioeconomic information is commonly displayed using decennial census information using choropleth mapping techniques. However, these data are aggregates of geographic units (census tracts or block groups) whose boundaries do not always reflect the natural distribution of human populations. A dasymetric mapping technique is one potential solution for mapping population density relative to residential land-cover. Dasymetric mapping depicts quantitative areal data using boundaries that divide the area into zones of relative homogeneity with the purpose of best portraying the underlying statistical surface.
Our objectives are to (1) use the USGS National Land Cover Datasets for 1992 and 2001 to classify homogeneous zones of high, low, and non-urban land cover; (2) utilize ancillary datasets such as slope, land ownership, and transportation to exclude uninhabited areas; (3) use a Visual Basic script to automate calculations in order to create a 30-meter surface grid of population; and (4) visually and statistically represent the new population-density values for the region within a temporal framework starting with 1990 and ending with 2000.
More information, data and tool downloads
Point of Contact: Rachel Sleeter
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U.S. Department of the Interior | U.S. Geological Survey
