-conn = pgdb.connect(host=options.host,
- database=options.database,
- user=options.username)
-
-cursor = conn.cursor()
-
-# We're ready to build our query, one step at a time. Firsy, we store
-# the Text->Geom conversion in a variable; this just makes the query a
-# little easier to read.
-geometric_object = "ST_GeomFromText('%s', %s)" % (args[0], options.srid)
-
-# We want to compute the population "under" the geometric object. We
-# can compute the percentage of a block that is covered by taking the
-# area of (the intersection of the object and the block) divided by
-# the total area of the block.
-#
-# Once we know the percentage covered, we just multiply that value by
-# the total population in the block to find the population that is
-# covered. The sum of these values over all blocks is our final
-# result.
-#
-query = """
-SELECT SUM(sf1_blocks.pop100 *
- ( ST_Area(ST_Intersection(%s, tiger.the_geom))
- / ST_Area(tiger.the_geom) )
- ) AS covered_population
-""" % geometric_object
-
-
-# Join our two block tables, so that we have both the demographic
-# and geometric data.
-query += \
-"""
-FROM (sf1_blocks INNER JOIN tiger
- ON sf1_blocks.tiger_blkidfp00 = tiger.blkidfp00)
-"""
-
-
-# We only need to calculate the covered population for the blocks
-# that actually intersect our object.
-query += \
-"""
-WHERE (ST_Intersects(%s, tiger.the_geom))
-""" % geometric_object
-
-
-# And we only take the first result, since they're all going to be the
-# same (our query returns the sum once for each block).
-query += \
-"""
-LIMIT 1
-"""