The quadtree is a tree-based data representation to store and index location information about a 2D image or area. The root of the tree has four branches corresponding to the four quadrants of the image. If there are no data points in any of these quadrants, then they are marked as empty. Otherwise the points are allocated to the relevant quadrant and then the same process is used to build a quadtree of those.
Defined on page 262
Used on pages 262, 263, 285
Quadtree representation of image