public boolean canPlace() {
    //  This only gets called just before entering the world, so I think I can
    //  put this here.  TODO:  Move the location-verification code from the
    //  TerrainGen class to here?  ...Might be neater.
    final World world = origin().world ;
    for (Tile t : world.tilesIn(area(), false)) {
      if (t == null || t.blocked()) return false ;
      if (type == TYPE_DUNE && t.habitat() != Habitat.DUNE) return false ;
    }
    return true ;
  }