quadkey

A quadkey is a hierarchical spatial indexing system used to partition a two-dimensional space, typically a map, into a grid of progressively smaller squares. This system is often employed in applications dealing with geographic data, such as mapping services and location-based services, to efficiently query and manage spatial information. The core principle of a quadkey is its recursive subdivision of space. A given area is first divided into four equal quadrants, often labeled north-west, north-east, south-west, and south-east. Each of these quadrants can then be further subdivided into four smaller quadrants, and this process can continue to an arbitrary level of detail.

The representation of a quadkey is typically a string of characters. Each character in the string corresponds to a specific quadrant at a particular level of subdivision. For instance, a '0' might represent the north-west quadrant, '1' the north-east, '2' the south-west, and '3' the south-east. A longer quadkey string indicates a smaller and more precise spatial area. This hierarchical structure allows for efficient spatial searching. To find all data within a certain region, one can identify the quadkeys that cover that region and then query only those specific spatial cells, rather than the entire dataset. This significantly reduces the amount of data that needs to be processed. Quadkeys are particularly useful for representing tiles in map systems, where each quadkey corresponds to a specific map tile at a certain zoom level.