code: private void net( WritableRandomIter hacksIter, WritableRandomIter netIter ) {
          // calculates the max order of basin (max hackstream value)
          pm.beginTask("Extraction of rivers of chosen order...", nRows);
          for( int r = 0; r < nRows; r++ ) {
              for( int c = 0; c < nCols; c++ ) {
                  double value = hacksIter.getSampleDouble(c, r, 0);
                  if (!isNovalue(value)) {
                      /*
                       * if the hack value is in the asked range 
                       * => keep it as net
                       */
                      if (value <= hackOrder) {
                          netIter.setSample(c, r, 0, 2);
                      } else {
                          hacksIter.setSample(c, r, 0, HMConstants.doubleNovalue);
                      }
                  }
              }
              pm.worked(1);
          }
          pm.done();
      }
docs: Return the map of the network with only the river of the choosen order.
  
  @param hacksIter the hack stream map.
  @param netIter the network map to build on the required hack orders.
  @return the map of the network with the choosen order.