I stumbled upon this excerpt as I was reading Graph Theory by Reinhard Diestel:
A polygon is a subset of $\mathbb{R}^2$ which is the union of finitely many straight line segments and is homeomorphic to the unit circle $S^1$, the set of points in $\mathbb{R}^2$ at distance 1 from the origin.
So based on this, how could any polygon be homeomorphic to $S^1$ even though both sets are of different cardinality?
Pardon me if the question is too basic; I'm totally new to topology and I probably am overlooking a detail.