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 --></style><title>overlap query</title></head><body>

<div>All:</div>

<div><br></div>

<div>I am trying to determine the amount (in hectares) of 1 or more

protected areas (parks) that overlap a watershed.</div>

<div><br></div>

<div>basically, what amount in hectares of a watershed that is

protected (falls within protected areas).  Both the Protected

Areas layer  (shape_pa) and Watershed Layer (shape_watershed) are

polygon layers (multipolygon) and have OID and GIST indexes. 

They also have the same SRID.</div>

<div><br></div>

<div>Though this doesn't calculate the hectares yet, so far its

returning nil.</div>

<div><br></div>

<blockquote>SELECT  shape_pa.name, shape_pa.the_geom from

shape_watershed, shape_pa</blockquote>

<blockquote>WHERE (shape_watershed.the_geom &&

shape_pa.the_geom) AND</blockquote>

<blockquote

>area2d(intersection(geometryn(shape_watershed.the_geom,0),geometryn(<span

></span>shape_pa.the_geom,0))) > 0 AND shape_watershed.name =

'Belize River'</blockquote>

<div><br></div>

<div>I was hoping this query would return the name of the protected

areas that overlap the watershed and their the_geom columns. Once I

got that far then I'd use it as a subquery to then calculate the

hectares as:</div>

<div><br></div>

<blockquote>SELECT sum(area(shape_pa.the_geom))/10000 as hectares

FROM</blockquote>

<blockquote>(</blockquote>

<blockquote>above query</blockquote>

<blockquote>);</blockquote>

<div><br></div>

<div>Any thoughts on why this isn't working?</div>

<div><br></div>

<div>Cheers,</div>

<div><br></div>

<div>Jerod Clabaugh</div>

<div>Belize Biodiversity Mapping Service</div>

<div>http://www.iwlearn.net/belize</div>

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