I'm really surprised I can't find information on this - I feel like I'm doing something very basic... What I want is all the nodes within a certain distance in the graph. I have a graph of half a million nodes and will only be visiting 20 or so - if you're curious, I have a graph of the street network in the Bay Area and will be looking at only those nodes within walking distance. So I read elsewhere that I need to inherit from default_dijkstra_visitor and throw an exception when I finalize a vertex beyond my search radius. I think I have this working. Now my problem is that I have to do this search many, many times - performance is very important - and I don't want to initialize the values for a half a million nodes when I'm only going to visit 20. I therefore want to use a std::map to store distances, and I want a key missing from that map to indicate an unvisited node, right? I also want to use dijkstra_shortest_path_no_init so as to skip initialization, but it's very hard to find documentation on this. I could post all my code here, but I'm not yet sure if that's the most efficient way to get my question answered. How does the no_init function work? Why doesn't it take a value for infinity? I feel like I need to pass DistanceMap.end() as my value for infinity so that a node not in the distance map looks like an unvisited node. Can anyone explain to me in words what I the no_init function expects me to pass to it? Thanks in advance! Fletcher