A subset $S$ of vertices in a planar graph $G$ is a free set if, for every set $P$ of $|S|$ points in the plane, there exists a straight-line crossing-free drawing of $G$ in which vertices of $S$ are mapped to distinct points in $P$. In this survey, we review - several equivalent definitions of free sets, - results on the existence of large free sets in planar graphs and subclasses of planar graphs, - and applications of free sets in graph drawing. The survey concludes with a list of open problems in this still very active research area.

翻译：设平面图 $G$ 的顶点子集 $S$ 为自由集合，若对于平面上任意 $|S|$ 个点构成的集合 $P$，总存在 $G$ 的一个直线无交叉画法，使得 $S$ 中的顶点映射到 $P$ 中的不同点。本文综述了自由集合的若干等价定义、平面图及其子类中大规模自由集合存在性的研究成果，以及自由集合在图绘制中的应用。最后，本文列出了该活跃研究领域中尚待解决的开放问题。