四元树又称四叉树是一种树状数据结构，在每一个节点上会有四个子区块。四元树常应用于二维空间数据的分析与分类。 它将数据区分成为四个象限。数据范围可以是方形或矩形或其他任意形状。这种数据结构是由 拉斐尔·芬科尔(Raphael Finkel) 与 J. L. Bentley 在1974年发展出来 。 类似的数据分割方法也称为 Q-tree。 所有的四元树法有共同之特点:

A quadtree is a tree data structure in which each internal node has exactly four children. Quadtrees are most often used to partition a two-dimensional space by recursively subdividing it into four quadrants or regions. The regions may be square or rectangular, or may have arbitrary shapes. This data structure was named a quadtree by Raphael Finkel and J.L. Bentley in 1974. A similar partitioning is also known as a Q-tree. All forms of quadtrees share some common features: