[postgis-users] area resulting from ST_Within

[surya]

Dear Fred,

Thank you very much. It works correctly !!. I try to further convert the area of  each district in a watershed as percentage to the watershed area in question. Please give me more help.

best regards,

surya
  ----- Original Message ----- 
  From: Fred Lehodey 
  To: PostGIS Users Discussion 
  Sent: Sunday, September 21, 2008 4:35 PM
  Subject: Re: [postgis-users] area resulting from ST_Within


  Hi Surya,
  you can try something like that:

  SELECT ws.name,dt.name, sum(ST_area(ST_intersection(ws.the_geom,dt.the_geom)))
  FROM  watersheds as ws, districts as dt
  WHERE ST_intersects(ws.the_geom,dt.the_geom)
  GROUP BY ws.name,dt.name
  ORDER BY dt.name

  Fred.



   
  On Sun, Sep 21, 2008 at 3:37 AM, surya <storma-ipb at indo.net.id> wrote:

    Dear List,

    I have two  tables, one table contains   5 polygons depicting 5 watersheds or river basin boundaries. Another table contain district bondaries. Using ST-contain function below, I have obtained districts belong to a certain watershed . My qestion is how to calculate area of each district contained in a certain watershed using sum(area)(), taking into consideration that one district might be splitted in two or more different watershed

    SELECT watersheds.name, districts.name
    FROM watersheds, districts
    WHERE ST_contains (watersheds.the_geom, districts.the_geom)
    GROUP BY watersheds.name, districts.name ;

    best regards,

    surya

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