title: In a GeoJson file, how do I combine features (states) into a single feature (region)
body: <p>I'm drawing a map of the US with D3.  Problem is the design on the project has changed and I need to draw regions as a whole instead of the individual states.  I can't for the life of me find any good info on how to combine state features into a single region feature.</p>
  
  <p>I'm assuming the gdal is the right tool for the job, but I can't seem to find how to do this.</p>