GET shapes

Fields to include with the response. Multiple fields **MUST** be a comma-separated (U+002C COMMA, ",") list. Note that fields can also be selected for included data types: see the [V3 API Best Practices](https://www.mbta.com/developers/v3-api/best-practices) for an example.

Filter by `/data/{index}/relationships/route/data/id`. Multiple IDs **MUST** be a comma-separated (U+002C COMMA, ",") list.

Max number of elements to return

Offset (0-based) of first element in the page

Results can be [sorted](http://jsonapi.org/format/#fetching-sorting) by the id or any `/data/{index}/attributes` key. Assumes ascending; may be prefixed with '-' for descending | JSON pointer | Direction | `sort` | |--------------|-----------|------------| | `/data/{index}/attributes/polyline` ...

Constraints: {'enum': ['polyline', '-polyline']}