Spatial data structures are great, and heavily used in all kinds of mapping applications. Most of the systems I've worked with used the more constrained quadtree structure, where the map is divided into uniformly-sized tiles, and a level-of-detail hierarchy is built. This is good for raster data, where each tile is a picture and the whole world is covered by tiles. The R-tree has great advantages when the complexity…
It is used in real-time defense systems, MMOs, and real-time location-based services.
[1]: paralleluniverse.co/spacebase/