Who’s On First is a gazetteer or a big list of places, each with a stable identifier and some number of descriptive properties about that location. An interesting way to think about a gazetteer is to consider it as the space where debate about a place is managed but not decided.

Who’s On First has been designed with the goal of ensuring longevity, portability and durability. What they means, in a nutshell, is:

  • An openly licensed data set, ranging from CC-0 (public domain) to CC-BY (attribution) at its most restrictive

  • Stable numeric IDs, meaning no semantics are encoded in the IDs

  • Plain-text GeoJSON records

  • Records are stored in a nested directory structure, derived from their IDs, making them comfortable and “at home” on the web

  • A finite set of placetypes, and a common set of ancestors for all records

  • A common set of core properties that can be supplimented with addition properties on a per record basis

  • Multiple geometries (because everyone disagrees about where neighbourhoods start of stop)

  • Records may be updated, superseded or deprecated but are never removed or replaced

  • All of the places whether they are big or small or important or “silly” depending on your point of view; Who’s On First is a tool for creating your own thresholds about “place” but is not meant to be the threshold itself

The Mapzen Places API allows developers (and robots) programmatic access to query and retrieve Who’s On First data via a REST-ish interface.

API methods are dispatched over HTTP with one or more query parameters and data is returned in response as JSON by default but you may also specify CSV or Who’s On First’s own meta formatted responses for certain API methods.

The endpoint for the Mapzen Places API is: https://places.mapzen.com/v1/

If you’re wondering the chances that there will ever be a /v2 are slim-to-never.

All errors are returned using HTTP status codes in the 400-599 range.

400 class errors mean the problem was on your end and 500 class errors mean the problem was our fault.


By default, API responses return simplified and trimmed version of the raw GeoJSON data for any given place. It is always possible to fetch an individual Who’s On First record from a stable permanent URL that can be derived from that record’s permanent ID.

The API is not feature complete yet, which is to say it will keep growing as time goes by. The easiest way to think about the Mapzen Places API is to look at the Who’s On First Spelunker website and imagine that anything you can do there to search and navigate all those places should also be possible via the API. As of this writing it is not but we’ll get there. If there is anything currently missing that you’d like or need to do sooner than later send up a flare and we’ll see about adding it to the list.

Some API methods are flagged as being experimental which means that both either their inputs or their outputs may change without warning. We’ll try not to introduce any backwards incompatible changes but you should approach these API methods defensively.

API Keys

To use the Mapzen Places API, you should first obtain a free developer API key.

Rate limits

See the Mapzen developer overview for more on API keys and rate limits.