[openstreetmap/openstreetmap-website] Snap to highways/cities on low-zoom placement of navigation markets (Issue #4649)

[Tom Hughes]

I think you're wrong about routing engines as I already explained...

OSRM's API is documented [here](http://project-osrm.org/docs/v5.24.0/api/#requests) and it has a several options like `radiuses` and `snapping` relating to matching locations to the routing graph. We don't currently set any of them.

Valhalla's API is documented [here](https://valhalla.github.io/valhalla/api/turn-by-turn/api-reference/) and it has a whole set of parameters like `radius`, `rank_candidates` etc that are all about how it matches locations to edges in the routing graph. The only one we currently set is `radius` which we set to five metres.

Graphhopper's API is documented [here](https://docs.graphhopper.com/#operation/getRoute) and although it doesn't seem to have a search radius it obviously does do snapping because it has parameters like `point_hint` and `snap_prevention` which influence the algorithm.

So it seems all three routers do in fact do some sort of snapping.

It may well be that we could tune the parameters that we pass to some of them better - if you do find better values then please do let us know and we can consider them.

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