Spatial Data Structure

A spatial data structure is one which is capable of storing and sorting objects based on multidimensional keys. The two-dimensional structures, such as the PR quadtree and PM quadtrees, can store objects based on two values, such as the longitude and latitude (x, y) of a city. In Java this is not a big deal, but in other languages, such as C and C++, it is. Note that latitude lines are horizontal, north and south of the equator, and correspond to lines with a fixed y coordinate, such as $y=30N$. Longitude lines are vertical, east and west of Greenwich, England, and correspond to lines with a fixed x coordinate, such $x=40W$. Three-dimensional structures, such as a K-d tree of order 3 or a PM octree, can store objects based on three values, such as the longitude, latitude, and sea level of a city (x, y, z).