How to download highways marked with a specific relation from OSM?

Question

There's an excellent general question about downloading canals here: How do I download specific OpenStreetMap data by tag?

There's also plenty of knowledge about OSM in general, but one thing I always struggle with is downloading 'highways' marked as a specific relation. The cycle network, for example, consists of many types of features joined together with a single relation: http://wiki.openstreetmap.org/wiki/Cycle_routes

How could one, for example, download the entire London Cycle Network in a single command?

Answer 1

Using Overpass turbo or the Overpass API, you get all national cycle routes that cross the Greater London border with

area["name"="Greater London"]->.boundaryarea;
(
relation(area.boundaryarea)[network=ncn];>;
);
out meta;

Don't try the same with larger areas, it will kill your browser.