A/B Street's map model as a platform

A/B Street's representation of a city, built mostly from OSM and lots of heuristics, is likely useful to other projects. This doc brainstorms what it would look like to properly expose it to other users.

To sum up what the map model provides: geometry + semantics.

Use cases

  • Different UIs (particularly 3D / VR) for exploring cities as they are or as they could be, like Streetmix 3D and Complete Street Rule
  • Importing slices of a city as assets into a game engine like Godot
  • A new OSM viewer/editor, particularly focused on POIs
  • Something focusing on 15-minute neighborhoods, with isochrones and nearby amenities

TODO: Give a quick Python example of what interacting with the end goal could look like.

Just data is not enough

At first glance, the existing Map structure could be written to some format with a nicely documented schema. This would certainly be useful, but it's not nearly enough. Interpreting the data sometimes requires lots of code, which already exists -- so why not expose it to users as well?

Examples in OSM where I wish "standard libraries" existed to interpret the data:

A/B Street solves these problems (or at least it tries to), but by itself, the resulting data isn't always useful. So some examples of where a library would be needed too:

  • Pathfinding. ABST does lots of work especially to handle "live" map edits and cheaply regenerate contraction hierarchies. Also, pathfinding requires obeying OSM turn restrictions that span multiple roads -- this prevents even plain old Dijkstra's from working correctly.
  • Getting geometry in different forms. Lanes are stored as a PolyLine, but what if a consumer wants the thickened Polygon, either as points, or maybe even pre-triangulated vertices and indices?

How would an API/library work?

The traditional approach is to link against part of A/B Street as a library and call it through language-specific bindings. The more language-agnostic option is defining an API (maybe JSON or protobuf) and having clients run a local A/B Street server, making HTTP requests to it. This is like the "sidecar" pattern in microservice-land.


Really have to think through this carefully. Some examples of big changes on the horizon:

  • Additive: separate cycleways and tramways. Likely no schema change.
  • Modify: traffic signals will get more complex
  • Modify: we'll likely try again to merge tiny intersections together, which would get rid of the current guarantees that a road/intersection is associated to one particular OSM object


Clients should be able to opt into different data layers. For example, A/B Street strips out OSM building tags right now to keep filesizes small. But an OSM viewer would want to keep this (and likely discard the large contraction hierarchies). So some pieces of the map model need to be teased apart into optional pieces, and probably loaded in as separate files.

The bigger vision

Depending what other open source projects are on board, the general idea is to start assembling an ecosystem of libraries/tooling to make it easier to build new things off of open GIS data.

The end state might look like this. A few separate applications would exist, all running both natively and in the browser:

  • A/B Street the game, more or less in its current form
  • A new OpenStreetMap viewer, likely focused on visualizing roads and points-of-interest in detail
  • The street parking OSM editor, and other OSM editors specialized for mapping certain things
  • A new app focusing on 15-minute neighborhoods, using isochrones to show amenities available nearby
    • Ideally, allow editing current land use / zoning, to let people explore how new policies might get closer to a 15-minute neighborhood.
    • Possibly GOAT does all of this already, and this new thing shouldn't be built
  • A new app for creating story maps, showing events that occur over time, with lots of detail about the surrounding environment

All of these would make use of some common libraries, which should be extracted out cleanly from A/B Street today:

  • the map model and OSM importer
  • the widgetry UI library
  • some common code for specifically interacting with maps in widgetry
  • a tool to generate a traffic demand model from OSM data, optional census data, etc
  • the discrete-event traffic simulation that A/B Street uses today
  • core geometry/utility libraries

But note only the first application would use things like the simulation library. The point of more cleanly modularizing these pieces is to make it easier for new people to build different pieces, without having to understand and be coupled to everything else. Also, as appropriate, these pieces should use common data formats (like shared-row) to be interoperable with Streetmix, Complete Streets, etc.