Expand description

map_model describes the world where simulations occur. Importing a map from OSM partly happens in convert_osm and here.

Helpful terminology:

Map objects are usually abbreviated in method names:

  • a = area
  • b = building
  • tr = transit route
  • ts = transit stop
  • i = intersection
  • l = lane
  • pl = parking lot
  • r = road
  • ss = stop sign
  • t = turn
  • ts = traffic signal


city 🔒
edits 🔒

Once a Map exists, the player can edit it in the UI (producing MapEdits in-memory), then save the changes to a file (as PermanentMapEdits). See https://a-b-street.github.io/docs/tech/map/edits.html.

make 🔒

See https://a-b-street.github.io/docs/tech/map/importing/index.html for an overview. This module covers the RawMap->Map stage.

map 🔒

A bunch of (mostly read-only) queries on a Map.

objects 🔒

Useful utilities for working with OpenStreetMap.

pathfind 🔒

Everything related to pathfinding through a map for different types of agents.


A business located inside a building.

Areas are just used for drawing.

A block is defined by a perimeter that traces along the sides of roads. Inside the perimeter, the block may contain buildings and interior roads. In the simple case, a block represents a single “city block”, with no interior roads. It may also cover a “neighborhood”, where the perimeter contains some “major” and the interior consists only of “minor” roads.

A building has connections to the road and sidewalk, may contain commercial amenities, and have off-street parking.

A single city (like Seattle) can be broken down into multiple boundary polygons (udistrict, ballard, downtown, etc). The load map screen uses this struct to display the entire city.

This is cheaper to store than a MovementID. It simply indexes into the list of movements.

A traffic signal consists of a sequence of Stages that repeat in a cycle. Most Stages last for a fixed duration. During a single Stage, some movements are protected (can proceed with the highest priority), while others are permitted (have to yield before proceeding).

An intersection connects roads. Most have >2 roads and are controlled by stop signs or traffic signals. Roads that lead to the boundary of the map end at border intersections, with only that one road attached.

This only applies to VehiclePathfinder; walking through these intersections is nothing special.

A road segment is broken down into individual lanes, which have a LaneType.

A lane is identified by its parent road and its position, ordered from the left.

Represents changes to a map. Note this isn’t serializable – that’s what PermanentMapEdits does.

A Movement groups all turns from one road to another, letting traffic signals and pathfinding operate at a higher level of abstraction.

A movement is like a turn, but with less detail – it identifies a movement from one directed road to another. One road usually has 4 crosswalks, each a singleton Movement. We need all of the information here to keep each crosswalk separate.

None corresponds to the native name

A way to refer to roads across many maps and over time. Also trivial to relate with OSM to find upstream problems.

Parking lots have some fixed capacity for cars, and are connected to a sidewalk and road.

A path between two endpoints for a particular mode. This representation is immutable and doesn’t prescribe specific lanes and turns to follow.

For callers needing to request paths with a variety of RoutingParams. The caller is in charge of the lifetime, so they can clear it out when appropriate.

A sequence of roads in order, beginning and ending at the same place. No “crossings” – tracing along this sequence should geometrically yield a simple polygon.

MapEdits are converted to this before serializing. Referencing things like LaneID in a Map won’t work if the basemap is rebuilt from new OSM data, so instead we use stabler OSM IDs that’re less likely to change.

Represents a specific point some distance along a lane.

Options for converting RawMaps to Maps.

A Road represents a segment between exactly two Intersections. It contains Lanes as children.

Tuneable parameters for all types of routing.

A Turn leads from the end of one Lane to the start of another. (Except for pedestrians; sidewalks are bidirectional.)

Turns are uniquely identified by their (src, dst) lanes and their parent intersection. Intersection is needed to distinguish crosswalks that exist at two ends of a sidewalk.

A contiguous set of roads with access restrictions. This is derived from all the map’s roads and kept cached for performance.


Businesses are categorized into one of these types.

Represent no parking as Private(0, false).

Who’s asking for a path?

One step along a path.

When pathfinding with different RoutingParams is done, a temporary pathfinder must be created. This specifies what type of pathfinder and whether to cache it.

See https://wiki.openstreetmap.org/wiki/Forward_%26_backward,left%26_right.

Either a lane or a turn, where most movement happens.


From some manually audited cases in Seattle, the length of parallel street parking spots is a bit different than the length in parking lots, so set a different value here.