Aim: use some modern methods and OSM to update the `route factor' (ratio of Euclidean to network distance) for UK
Snippet from Dan's PhD:
A simple way to describe the discrepancy between route distance and straight line distance is with a ‘route factor’ (see e.g. Chapman 1979 p.215; Black 2003 p.68). This is simply the ratio of the distance between points along a network route over the Euclidean distance between those points. This value approaches one as the two measurements converge, implying network density is increasing - and Euclidean approximations can do a better job. There is a well-established correlation between network density and development levels (Chapman 1979 p.220), and this is reflected in the route factor: it approaches one in more developed countries - though even that assumption breaks down at small enough scales.