We
argue that the basic typology of spatial boundaries involves an opposition
between bona fide (or physical) boundaries on the one hand, and fiat boundaries
on the other, the latter being exemplified especially by boundaries induced
through human demarcation, for example in the geographic realm. The classical
metaphysical problems connected with the notions of adjacency, contact,
separation and division can be resolved in an intuitive way by recognizing
this two-sorted ontology of boundaries. Bona fide boundaries yield a notion
of contact that is effectively modeled by classical topology; the analogue
of contact involving fiat boundaries calls, however, for a different account,
based on the intuition that fiat boundaries do not support the open/closed
distinction on which classical topology is based. In the presence of this
two-sorted ontology it then transpires that mereotopology—topology erected
on a mereological basis—is more than a trivial formal variant of classical
point-set topology.
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