This example adapts mbostock's quadtree brushing demo to find the nearest neighbor (shown red) of a new point (shown yellow). Choose a new point to classify by clicking on the diagram. (An alternative approach for nearest neighbors of the mouse position is D3's Voronoi polygons, but the idea here would extend to rapidly classifying many new points against a base collection of points.)

We use a data-dependent order of recursion through the quadtree