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I have two polygons in PostGIS that have incongruities. One polygon (the yellow one) is legal county boundaries. The other polygon (blue) is essentially neighborhoods. 98% of the lines align perfectly. The other 2% don't align because the boundaries have changes but not been updated on the neighborhoods polygon.

My question: Using either PostGIS (preferred) or QGIS, how can I "snap" the neighborhood boundaries to the county boundaries? I've tried:

ST_Multi( ST_Intersection(neighborhoods.geom, county.geom) ) END AS geom

EDIT: This query "worked" in that it prevented neighborhoods from bleeding into incorrect counties, but it just removes the area that causes the bleed creating blank spaces inbetween boundaries.

snap

LearnWorkLearn
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  • I would love to see anyone with a postgis solution as well. – tilt Aug 06 '17 at 16:58
  • For those who arrived here seeking a PostGIS solution, here's what I've arrived at:

    SELECT b.block, p.county_name, p.district_id ST_AREA(CASE WHEN ST_CoveredBy(b.geom, p.geom) THEN p.geom ELSE ST_Multi(ST_Intersection(b.geom, p.geom)) END) AS geom FROM blocks b INNER JOIN district p ON (ST_Intersects(b.geom, p.geom) AND NOT ST_Touches(b.geom,p.geom))

    From there, I ranked the area column, accepted the top ranked area, and forced a p.county_name=b.county_name match. This is not an ideal solution because it's highly specific to my use case, but may provide help to others.

     – LearnWorkLearn Aug 28 '17 at 15:31

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