OGC WMS

WMS predates most of what the modern API conversation takes for granted, and it got one thing conspicuously right: the service describes itself. A GetCapabilities request returns a machine- readable document listing every layer, every supported coordinate reference system, every output format and every bounding box the service can serve. That is a discovery document, shipped as a standard, in 1999.

• Self-describing by default - GetCapabilities is not optional and not an afterthought. It is how a client learns what exists.
• Three core operations - GetCapabilities, GetMap, and optionally GetFeatureInfo.
• 1.3.0 is also ISO 19128 - which is why it turns up in government procurement and national spatial data infrastructure requirements.
• Image out, not data out - WMS returns rendered maps. Its siblings WFS and the newer OGC API family return the underlying features.

What the evidence shows

The State of Canadian Travel APIs found WMS in an unexpected place: Transport Canada, the aviation safety regulator, publishes OGC WMS 1.3.0 with a validated GetCapabilities, alongside the CKAN Action API and Esri ArcGIS REST as a de facto interface, all under the Open Government Licence – Canada — worldwide, royalty-free, perpetual, commercial use permitted, nothing to sign.

In a market where eight of nine organizations score zero on governance and only one publishes a machine-readable contract, Transport Canada is the only unconditionally open organization in Canadian travel, and it got there by adopting general-purpose open geospatial and open-data standards rather than anything the travel industry produced.

That pattern repeats across the quartet: the organizations with genuinely reachable interfaces are regulators and standards bodies using standards from outside travel — WMS, CKAN, GTFS, OpenAPI — while the sector’s own standards sit behind accreditation, certification and commercial agreement. The most open thing in travel is usually not a travel standard.