consider the problem: given a graph and a number of vertices $n$ less than the vertices in the graph, and a distance $d$. find a set of $n$ vertices such that all vertices of the graph are within $d$ distance of the $n$ vertices (measured in edge count of the shortest path). in a sense the $n$ vertices are "hubs" of the graph. (there may be other constraints on their selection.) suspect this problem may arise in a variety of guises. am not nec. looking for an exact solution.
looking for the contexts this arises (applications) & recent literature/survey(s) on this problem, finding the "natural" "hubs" of a graph.
possibly somewhat related is finding/adding a few edges to yield "good" hubs (hub sets that are small relative to the vertices they "reach").