protected boolean checkLandingArea(World world, Box2D area) {
    if (dropPoint instanceof Venue) {
      return dropPoint.inWorld() ;
    }
    else for (Tile t : world.tilesIn(area, false)) {
      if (t == null) return false ;
      if (t.owner() == this) continue ;
      if (t.owningType() > Element.ELEMENT_OWNS) return false ;
    }
    return true ;
  }