code: public Rectangle2D getBounds () {
          Rectangle2D ret = null;
  
          for (Stop stop : feed.stops.values()) {
  
              // skip over stops that don't have any stop times
              if (!feed.stopCountByStopTime.containsKey(stop.stop_id)) {
                  continue;
              }
              if (ret == null) {
                  ret = new Rectangle2D.Double(stop.stop_lon, stop.stop_lat, 0, 0);
              }
              else {
                  ret.add(new Point2D.Double(stop.stop_lon, stop.stop_lat));
              }
          }
  
          return ret;
      }
docs: Get the bounding box of this GTFS feed.
  We use a Rectangle2D rather than a Geotools envelope because GTFS is always in WGS 84.
  Note that stops do not have agencies in GTFS.