title: how do i remove overlapping lines in postgis
body: <p>I have a typical database with millions of polygons as land parcels and i want to split these polygons onto lines and then remove the lines that overlap eachother. These lines will be used purely for rendering in mapnik/and or geoserver as at the moment every parcel boundary gets rendered twice. </p>
  
  <p>i propose to split the parcel polygons into a new table ("boundary_lines") and then search and remove overlapping lines. how would i go about removing these overlapping lines in postgis? </p>