If you travel within a city from A to B, how different is the geometric distance (as the crow flies) and the length of the shortest path following the road network? For the 4 largest municipalities of the Netherlands (Amsterdam, Rotterdam, The Hague, and Utrecht) I randomly samply a large number of intersections and construct the straight lines and road network shortest-paths between these nodes, and compare their total lengths. tl;dr; they are highly correlated.