[michaelt]

You can visualise a graph with 9 billion nodes on https://www.openstreetmap.org :)

You could copy their design, if you know how you want to project your nodes into 2D. Essentially dividing the visualisation into a very large number of tiles, generated at 18 different zoom levels, then the 'slippy map' viewer loads the tiles corresponding to the chosen field of view.

Then a PostGIS database alongside, letting you run a query to get all the nodes in a given rectangle - such as if you want to find the ID number of a given node.

[vbrandl]

I would guess OSM uses optimizations for eucledian graphs, where the path a->c is always shorter than a->b->c. This restriction makes e.g. TSP solvable. But this property does not hold for any generic graph. I don't know if this makes visualisation also easier.

[michaelt]

Technically, if you've got a bumpy dirt track a->c and a freeway a->b->c then the travel time on the latter route can be shorter.

Of course, they do get to dodge a major problem: That high-dimensional data is hard to visualise in an understandable way. Everyone knows what a map looks like, nobody knows what a clear visualisation of a set of 100-dimensional vectors looks like.