Overpass turbo bbox - reducing amount of data for a relation with many ways

Question

I am trying to query on hiking routes http://overpass-turbo.eu/s/q52 using the following centred on London.

[out:json][timeout:25];
relation["route"="hiking"]({{bbox}});
out geom;

I am finding I getting data I don't want which has a performance impact. I think I have two issues.

Some of the relations are very big. (3212473 Greenwich Meridian Trail 20469 Thames Path)
I am getting relations that are way outside my viewport (Shakespeare's Way - 71448) and I can't see why.

On point 1., can I process the relation - eg only output the ways that appears in my viewport. If I am interested in London I dont want details of the route near lincoln.

Answer 1

If you want all relations being tagged with route=hiking but only those ways of those relations which are inside your bounding box, you should try following query:

[out:json][timeout:25];
// Store all interesting relations which intersect with the bounding box in
// a set called "interestingrelations".
relation["route"="hiking"]({{bbox}})->.interestingrelations;
// Store all way members of the relations in the set "interestingrelations"
// in the set "alltheirways".
way(r.interestingrelations)->.alltheirways;
// Filter "alltheirways" using a bounding box filter. Store result in "waysinside".
way.alltheirways({{bbox}})->.waysinside;
// Output geometry of "waysinside".
.waysinside out geom;

Features of Overpass QL in use:

Overpass turbo bbox - reducing amount of data for a relation with many ways

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