A space can be compactified by adding a point at infinity. The point of this abstraction, as with abstraction in general, is not so much generalization as unification.

Points can now be represented as circles with infinitesimal radius. Lines can be represented as circles with infinite radius. Circles (the normal ones) can be thought of as circles with finite radius.

So time may be a flat circle, but that doesnâ€™t imply it repeats (in a finite amount of time) =).