Making maps connectable: stable, non-proprietary IDs and data standards for streets
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README.md

SharedStreets Referencing System

Introduction

SharedStreets data standards are a way to uniquely identify street space and connect data related to streets. SharedStreets makes maps connectable, and allows porting of data between different street representations, whether data linked to OpenStreetMap, a city-managed GIS system, or a commercial basemap.

Cities today depend on geographic information systems (GIS) to collect and share street data, but this process requires users to agree on a map, or to use predefined, and often proprietary IDs to describe streets.

This limits the potential for collaboration and data sharing between government agencies, and with the private sector. And use of proprietary maps and identification systems can undermine cities’ ability to use and share critical public information about streets.

SharedStreets provides a global, non-proprietary system for describing streets, designed to incorporate any source of street-linked data. This allows public and private entities to communicate with clarity and precision about streets while ensuring full compatibility with organizations’ internal map data.

GIS vs SharedStreets data exchange

The SharedStreets referencing system was originally created as part of the OpenTraffic project, as a mechanism for sharing dynamic traffic information. SharedStreets builds on the core concepts from OpenLR and provides a collection of data formats and open source tools to re-imagine collaboration and sharing of street-linked data.

The SharedStreets referencing system is being released as a draft proposal, along with data samples and tools for generating references from OpenStreetMap and Shapefile data sources. Comments and suggestions on the format will be managed via this Github repository. Please open an Github issue or pull request to contribute.

A production version of the SharedStreets Referencing System and a global data set will be released soon. During the preview phase, referencing data can be generated using open source tools for any location.

Example Applications

Traffic data: SharedStreets references are used to share basemap-independent descriptions of traffic conditions. In the OpenTraffic project fleet operators convert GPS data to to traffic observations (speeds along OpenStreetMap defined roadway segments). Traffic observations are shared externally using SharedStreets references to describe street segments.

Street and curb inventory: Cities produce detailed curb inventories (e.g. parking regulations and physical assets) using internally managed linear referencing systems (LRS), or latitude/longitude coordinates not linked with streets. Internal LRS data can be translated to SharedStreets references to allow interoperability with other city or external data sets.

Incident/road closure reporting: transport authorities share data about street conditions in real-time with consumer applications. SharedStreets references can be used to streamline reporting procedures by providing a shared, non-proprietary format for describing roadway incidents and closure events.

Core Concepts

The SharedStreets Referencing system is built on four layers of data:

  1. SharedStreets References: basemap-independent references for intersection to intersection street segments
  2. SharedStreets Intersection: nodes connecting street street segments references
  3. SharedStreets Geometries: geometries used to generate street segment references
  4. OSM Metadata: underlying OSM way and node references used to construct SharedStreets data

Segment references

The OpenLR-style street segment references are the foundation of the SharedStreets Referencing System. These references allow users to uniquely describe any street segment in the world using just a few high-level characteristics.

This allows users with different map geometries to describe the same street segments in identical or nearly identical terms. The references are used to find matching streets in users' existing internal maps. In cases where no matching street is found, users have the opportunity to update their map data to fill in missing or incorrectly mapped segments.

Street segment references protect users' intellectual property, as data can be shared without disclosing a complete map. Segment references also enable rapid reconciliation of data derived from different maps.

BYOM

SharedStreets is based on the idea that users will maintain their own internal basemaps. Any basemap--open or proprietary--can generate SharedStreets references for sharing with others using a different map. With open basemap data users are encouraged to share the full set of SharedStreets data layers (references, geometries and metadata). Users with proprietary basemap data can share only the segment references, allowing exchange of information while protecting map street geometries and other intellectual property.

Stable, non-proprietary shorthand IDs

SharedStreets uses 128-bit shorthand identifiers to relate data within the SharedStreets referencing system. These IDs provide a basemap-independent addressing system for street segment references, intersections and geometries. These identifiers are generated deterministically using a hash of the underlying data. This means that two different users with the same input data can generate matching SharedStreets identifiers. This simplifies data sharing, allowing users to match data using shorthand IDs whenever possible.

In the draft specification the 128-bit IDs are encoded as base-16 (hex) strings.

Generating references + data tiles

SharedStreets street references, intersections and geometries can be generated from OSM data using the SharedStreets Builder application.

As part of the draft release pre-generated a sample of SharedStreets tiles for New York City are included in this repository. A zip archive of the full NYC tile set can be downloaded here (146MB file). Users can generate their own tiles for any arbitrary OSM data set using the SharedStreets Builder application.

Once the data specification is finalized the SharedStreets program will generate and maintain a global data tile set, and provide tools to cities for reconciling their data with the referencing system.

The draft release of SharedStreets exports data as JSON files, cut into mercator tiles at zoom level 10. These draft tiles are verbose and are designed to support exploration and refinement of the specification. Once the specification is finalized SharedStreets will provide JSON and Protocol Buffer tile formats. SharedStreets is also exploring use of "lossy" vector tile formats for distribution of data for web visualization.

DRAFT ShareStreets Data Formats

Changelog

2017-10-20: Initial release for comments, using JSON tile representation.

2017-11-10: Updated spec to include "inbound" and "outbound" bearings for references, backwards compatible with OpenLR-derived data standards while allowing for more complex geometry matching workflows. (Thanks to @migurski and @remix for this suggestion.)

2017-11-20: Switched from JSON to protocol buffer encoded tiles as default output format.

2018-01-14: Switched IDs to base-16 (hex) encoding. Release of updated sharedstreets-builder application (v0.1.2) and sample tile set.

Protocol Buffer Encoding

SharedStreets encodes reference data in protocol buffer encoded map tiles. The encoding format, described here, targets the Protocol Buffer v3 format, and uses the following conventions to enable efficient data storage:

  • "Oneof" wrappers allow null values for optional fields. This allows for space-efficient values, while ensuring that downstream users can differentiate between zero and null values for bearings and lengths.

  • Strings of latitude/longitude values for geometries are encoded as a single stream of values (e.g. "[-74.003388, 40.634538],[-74.004107, 40.63406]" is encoded as "-74.003388,40.634538,-74.004107,40.63406".

  • Distances are encoded in centimeters using int32 field types.

For more information about encoding see the SharedStreets Builder application, which converts OpenStreetMap and other geospatial data into SharedStreets protocol buffer tiles.

SharedStreets Intersections

GIS vs SharedStreets data exchange

{
	"type": "Feature",
	"properties": {
		"id": "5gRJyF2MT5BBErTyEesQLC",
		"osmNodeId": 42460951,
		"outboundReferenceIds": ["6mjqqv7YNsp4541DmrrRbV", "jwwKcUvHuCw6GJJAT3mDQ", "2Vw2XzW4cs7r32RLhQnqwA"],
		"inboundReferenceIds": ["VmSkhzGKoEc767w98x35La", "VXKSEokmvBJ81XHYhUronG", "B7RPzs3hb1cSXqYcAKmUhE"]
	},
	"geometry": {
		"type": "Point",
		"coordinates": [-74.003388, 40.634538]
	}
}
{
	"type": "Feature",
	"properties": {
		"id": "N38a21UGykpnqxwez7NGS3",
		"osmNodeId": 42460956,
		"outboundReferenceIds": ["VXKSEokmvBJ81XHYhUronG", "KxeV6ycjnarJU8pGEmkUx9", "V6aRcYcZgd5D58GaEaxCaF"],
		"inboundReferenceIds": ["8ShvkUbHhu1SXzcE5XMj2L", "Ak3c8QdsYWVRn5Ap53hzcH", "2Vw2XzW4cs7r32RLhQnqwA"]
	},
	"geometry": {
		"type": "Point",
		"coordinates": [-74.004107, 40.63406]
	}
}

SharedStreets References

GIS vs SharedStreets data exchange

SharedStreets References (SSR) are directional edges in a road network. Two-way streets have two SSRs, one for each direction of travel, while one-way streets only have one SSR. In the draft specification these are labeled "forward references" and "back references," with the forward reference following the direction of the map geometry used to generate the references.

Each SharedStreets Reference consists of two or more location references (LRs) that describe the latitude and longitude of the beginning or end of a street segment. SSRs also describe type of road (or the "form of way," as defined by OpenLR), and length of the geometry connecting location reference points. In combination these attributes uniquely describe any road segment, and can be used to look up corresponding streets in users’ internal maps.

Forward Reference

{
	"id": "2Vw2XzW4cs7r32RLhQnqwA",
	"geometryId": "NxPFkg4CrzHeFhwV7Uiq7K",
	"formOfWay": 3,
	"locationReferences": [{
		"sequence": 1,
		"point": [-74.003388, 40.634538],
		"bearing": 228.890377,
		"distanceToNextRef": 80.730221,
		"intersectionId": "5gRJyF2MT5BBErTyEesQLC"
	}, {
		"sequence": 2,
		"point": [-74.004107, 40.63406],
		"intersectionId": "N38a21UGykpnqxwez7NGS3"
	}]
}

Back Reference

{
	"id": "VXKSEokmvBJ81XHYhUronG",
	"geometryId": "NxPFkg4CrzHeFhwV7Uiq7K",
	"formOfWay": 3,
	"locationReferences": [{
		"sequence": 1,
		"point": [-74.004107, 40.63406],
		"bearing": 48.890138,
		"distanceToNextRef": 80.730221,
		"intersectionId": "N38a21UGykpnqxwez7NGS3"
	}, {
		"sequence": 2,
		"point": [-74.003388, 40.634538],
		"intersectionId": "5gRJyF2MT5BBErTyEesQLC"
	}]
}

Notes:

  • For long segments LRs are repeated every 15km, segments shorter than 15km have only a beginning and end LR.
  • LRs describe the compass bearing of the street geometry for the 20 meters immediately following the LR. The final LR of a SSR does not provide a bearing.
  • An initial set of SSRs are built using OpenStreetMap (OSM) data, however, in the future SharedStreets users will be able to publicly register SSRs for streets not found in OSM. These could include data found in commercial or government maintained basemaps. Users do not have to share the underlying data, only the SSR descriptor.

SharedStreets Geometries

GIS vs SharedStreets Geometries

SharedStreets Geometries are street centerline data derived from the basemap used to produce SharedStreets References. A single geometry is shared by each set of forward and back references.

SharedStreets is premised on the idea that there's no one correct geometry for a given street. Just as street references can be generated from any basemap, street geometries can be derived from any data source.

{
	"type": "Feature",
	"properties": {
		"id": "NxPFkg4CrzHeFhwV7Uiq7K",
		"fromIntersectionId": "5gRJyF2MT5BBErTyEesQLC",
		"toIntersectionId": "N38a21UGykpnqxwez7NGS3",
		"forwardReferenceId": "2Vw2XzW4cs7r32RLhQnqwA",
		"backReferenceId": "VXKSEokmvBJ81XHYhUronG",
		"roadClass": 3
	},
	"geometry": {
		"type": "LineString",
		"coordinates": [
			[-74.003388, 40.634538],
			[-74.003621, 40.634383],
			[-74.003621, 40.634383],
			[-74.004107, 40.63406]
		]
	}
}

SharedStreets OSM Metadata

SharedStreets generates metadata about the map data used to generate references and geometries. For OSM-derived references the way and nodes are stored as part of metadata layer. This simplifies matching references back to underlying basemap data, and provides a framework to easily track changes in the underlying basemap data.

{
	"geometryId": "NxPFkg4CrzHeFhwV7Uiq7K",
	"waySections": [{
		"wayId": 420584810,
		"roadClass": 3,
		"oneWay": false,
		"roundabout": false,
		"link": false,
		"nodeIds": [42460951, 4205392123]
	}, {
		"wayId": 420584817,
		"roadClass": 3,
		"oneWay": false,
		"roundabout": false,
		"link": false,
		"nodeIds": [4205392123, 42460956]
	}]
}

Frequently Asked Questions

How does this relate to OpenStreetMap? (Or, doesn't OSM already do this?)**

SharedStreets complements OpenStreetMap. OSM does not attempt to provide stable IDs, and complex OSM ways make many applications difficult to build using raw OSM data.

SharedStreets provides a layer of abstraction on top of OSM, allowing users to work with the topology of OpenStreetMaps data without dealing with the details how OSM ways are encoded.

By providing direct references to OSM way and node IDs users can always query and relate SharedStreets references back to the underlying OSM data where needed.

We believe that SharedStreets will allow users to more rapidly improve OpenStreetMap data by making it easier to identify missing streets, or opportunities to improve street geometry and connectivity.

How does SharedStreets relate to OSMLR v1.x?

OSMLR v1.x was developed to support OpenTraffic under contract from the World Bank. SharedStreets is the continuation of this work as part of the Open Transport Partnership. The SharedStreets Referencing system is effectively "OSMLR v2.0" but drops the OSMLR name as it intends to support broad range of map data formats including, but not limited to, OpenStreetMap. SharedStreets also addresses two critical deficiencies in the OSMLR v1.x spec, documented here.