I've been thinking a possible approach to mapping if we start with routes that are good enough to be safe for children to cycle, we'd see the missing links to join up. An example by Mark: https://aseasyasridingabike.wordpress.com/2017/01/16/plotting-a-dutch-network-onto-a-british-town/ A lot more work for a big city though! Rachel has talked about doing this for London: http://rachelaldred.org/projects-2/the-london-cycleable-network-map/. Perhaps it possible to automatically import the streets labelled as "quiet", prune as necessary and add other cycle routes like the old rail lines and canal paths.