The problem in computational geometry of identifying the point from a set of points which is nearest to a given point according to some measure of distance. The nearest neighborhood problem involves identifying the locus of points lying nearer to the query point than to any other point in the set.
The nearest neighbor from the set of points , can be computed in the Wolfram Language using Nearest[u1, u2, ..., , x].
An extensive site of nearest neighbor material is maintained by Lifshits.