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Dasymetric Mapping and Areal Interpolation


Case Study: Delaware County, Pennsylvania


Here, population data for Delaware County, Pennsylvania are dasymetrically mapped using remotely sensed land cover data. 


Population data were acquired from the U.S. Bureau of the Census for the year 2000 at the tract level.  There are 148 tracts.  A map of the original tract boundaries appears below.



A map of the tract level population density appears below.



The ancillary land cover data were derived from the U.S. Geological Survey National Land Cover Data (NLCD) program.  These raster data were derived from 2001 Landsat ETM+ imagery.  For the dasymetric mapping, these data were smoothed using a majority filter and converted to vector format.  This resulted in a vector data layer with 3,526 polygons.  A map of the land cover data is given below.



The dasymetric mapping was applied using a 'containment' sampling method with no preset class densities and no regions.  This procedure produced a new vector data layer with 4,745 polygons.  The dasymetric map of population density is given below.  In the western, rural part of the county population are assigned to the developed areas at the expense of the agricultural and forest areas.  In the eastern, urban areas population are assigned to the developed areas at the expense of areas of water and wetland cover.