Algorithm::QuadTree implements a quadtree algorithm (QTA) in pure Perl. Essentially, a QTA is used to access a particular area of a map very quickly. This is especially useful in finding objects enclosed in a given region, or in detecting intersection among objects. In fact, I wrote this module to rapidly search through objects in a Tk::Canvas widget, but have since used it in other non-Tk programs successfully. It is a classic memory/speed trade-off.

Lots of information about QTAs can be found on the web. But, very briefly, a quadtree is a hierarchical data model that recursively decomposes a map into smaller regions. Each node in the tree has 4 children nodes, each of which represents one quarter of the area that the parent represents. So, the root node represents the complete map. This map is then split into 4 equal quarters, each of which is represented by one child node. Each of these children is now treated as a parent, and its area is recursively split up into 4 equal areas, and so on up to a desired depth.