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census data w/ local shapefile

September 19 2011 | 0 comments
Categories: Map Data

I have a polygon shapefile showing all civic leagues in a city. I need to add population data to the civic leagues. I think I need to download either census blocks or tracts and then dissolve or clip the layers. So what exactly do I need to do to add population data from the census files to the civic league shapefile?

Mapping Center Answer:

You need to apportion the population data from census polygons to your civic league polygons.  First, add a new field to the census polygon attribute table and then use Calculate Geometry to add a field that contains the size of the area. Then, Intersect your two datasets to create a new shapefile. Export the attribute table, add a new field and calculate the size of the area using the same process as before.  You can then calculate the population for each new area by creating another new field and calculating the different between the old and new areas that exist in your attribute table, multiplied by the population.  The equation in the Field Calculator would look something like POPULATION =(NEW SHAPE AREA/CENSUS AREA) * POPULATION. You should then have a field with the correctly apportioned population data for your civic league areas.

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