Extension for per-node attributes

It would sometimes be useful to have per-node attributes within a LineString, MultiLineString, Polygon, or MultiPolygon feature, for example to link these nodes back to the OSM IDs that they came from.

I'm thinking this could look in GeoJSON something like this:

{ "type": "Feature", "properties": { ... }, "geometry": " { ... },
  "linear-attributes": [ null, null, { "node": 12345 }, { "node": 56789, "way": 66 }, null, { "node": 55 }, null ] }

where there the linear-attributes array has the same structure as the geometry.coordinates array, and each element is either null if there is no attribute, or a set of key-value pairs if there are attributes. (Or some other syntax if anybody has any better idea.)

In the vector tile, it could be part of the Feature:

repeated sint linear_attributes = 5 [ packed = true ];

where each positive number represents a key or value in the layer attributes, like in the keys, and each negative number represents (forward) motion through the geometry, so the above would be encoded as:

-2 (move 2),
0 (node), 0 (12345), -1 (move 1),
0 (node), 1 (56789), 1 (way), 2 (66), -2 (move 2),
0 (node), 3 (55), -2 (move 2)

Alternately we could define new geometry types where each position contains x and y coordinates followed by a count of attributes and a set of key-value references, since the parallel arrays might be awkward to maintain.

Any opinions on this idea?

Review the proposed GeoJSON linear-attributes structure and the vector-tile linear_attributes encoding described in the issue. Compare the alternatives and determine whether the specification has enough consensus to define a concrete extension; done would require an agreed design rather than only an implementation preference.