title: mapnik geojson vector tiles
body: <p>Could you point me in the right direction on how to create vector tiles from geojson or topojson?
  mapnik-vector-tile seems to be the right library but I cannot find a good example.
  There seems to be examples of geojson files (14_2620_6331-XXX) but how did the pbf files get created?
  Thanks.
  Pat.</p>