Population within a half-mile of trains in Pennsylvania, summarized by county and municipality.
Population within a half-mile of trains in Pennsylvania.  Calculations were made using 2010 Census Tract (CT) level data, train locations, and municipal and county shapefiles.  All area calculations were performed in Albers Equal Area -Great Lakes projection.  The process for generating the population estimates were as follows:
1.  Form a half mile buffer around active freight lines in and near Pennsylvania
2.  Clip CT data to buffer generated in step 1, resulting in a new layer (CT-clip)
3.  Determine the ratio of square miles of fragments in CT-clip to the full CT polygons.
4.  Multiply ratio in step 3 by population data in CT file
5.  Forge a union between CT-clip and county layer
6.  Select and export records with data from both layers
7.  Calculate population of the new fragments by repeating steps 3-4
8.  Merge fragments based on common county.  Population is the sum of these fragments, within any given county.
9.  Repeat steps 5-9, using municipal data instead of county data.
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