An interesting character of the organisational border is that two contradictory elements of what a borders means exist simultaneously. And in some way one cannot exist without the other.
On the one hand there is the fact that a border separates, that is the nature of the border. That is why some belong to the organisation and others do not.
On the other hand organizations are meaningless unless they connect with the outside world. Organisation have by their very existence impact on the environment.
In the design of organisation both aspects matter. The question which elements dominates is not so relevant.