Don’t you just love getting CAD data into GIS! I received a .dwg file with study areas delineated as polylines which we needed as polygons for analysis purposes. And it wasn’t just one polyline surrounding each study area … there were hundreds of little line segments which outlined a couple dozen areas (what was this CAD tech thinking?) . Luckily each segment had a name to associate it with the proper area.

I found that ArcMap’s tools for doing this are painfully inadequate so I turned to postgis. After converting the dataset to a shapefile, the solution was simple:

shp2pgsql “study_areas.shp” areas | psql -d gisdata pgsql2shp -f “study_areas_poly.shp” gisdata \ “SELECT BuildArea(collect(the_geom)) AS the_geom, name FROM areas GROUP by name”

Viola… a new shapefile with my proper polygons instead of CAD chicken scratch.