def asTuple(self):
        """Return the location as a tuple.
        Sort the dimension names alphabetically.
        ::
        
            >>> l = Location(pop=1, snap=-100)
            >>> l.asTuple()
            (('pop', 1), ('snap', -100))
        """
        t = []
        k = sorted(self.keys())
        for key in k:
            t.append((key, self[key]))
        return tuple(t)