Well-deployed technologies

Generic options for writing spatial data

There are several generic options for writing spatial data which are established standards:

  • GeoJSON is a widely used format which is serialized in JSON and easy for browser-based Web applications to process, but supporting only one coordinate reference system (CRS84 - i.e., WGS 84 longitude/latitude), and geometries up to 2 dimensions (points, lines, surfaces).
  • Geography Markup Language (GML) provides the ability to express any type of geometry, in any coordinate reference system, and up to 3 dimensions (from points to solids) but is typically serialized in XML.
  • GML Simple Features offers a profile of GML: a subset of the myriad of possibilities GML itself offers. The profile contains the most common geometry types as well as restricting the XML structures that may be used.
  • GeoSPARQL is an extension of SPARQL, offering geographic query operators, but it also defines a basic ontology for geography, which can be used for publishing spatial linked data.
  • GeoRSS is a lightweight way to extend existing RSS feeds with simple geographic information. It is an OGC-endorsed community standard.
  • Keyhole Markup Language (KML) can be used to represent spatial things and 0D-3D geometries, mainly focussed on spatial data visualization and interaction in so-called 'earth browsers'.

Semantic standards: vocabularies

The Semantic Sensor Network Ontology (SSN) is an ontology for describing sensors and their observations, the involved procedures, the studied features of interest, the samples used to do so, and the observed properties, as well as actuators. SSN includes a lightweight core ontology called SOSA (Sensor, Observation, Sample and Actuator) that is able to support a wide range of applications and use cases, including satellite imagery, large-scale scientific monitoring, industrial and household infrastructures, social sensing, citizen science, observation-driven ontology engineering, and the Web of Things. SOSA can be used without any reference to the full SSN ontology, which adds numerous classes, properties and axioms to SOSA and can be used for advanced linked data use cases. SSN is underpinned by Observations & Measurements, an ISO and OGC standard for describing observations and measurements made by sensors.

The Time Ontology contains concepts for describing the temporal properties of resources in the world or described in Web pages, including relations between time instants and intervals, information about durations, and temporal position including date-time information. Not only the conventional (Gregorian) calendar and clock can be used: other temporal reference systems are also possible.

To represent multi-dimensional data on the Web as linked data, the RDF Data Cube Vocabulary is available. An extension for spatial and temporal data exists, but that part is still exploratory work.

Geometry

Well Known Text (WKT) is a compact format to represent geometry literals, used in GeoSPARQL and other spatial data representation formats, and supported in most triple stores and some web libraries. Geohash is a convenient way to express a location using a short alphanumeric string. It only supports 0-dimensional geometries (points).

Reference locations

There are different ways to reference a location. One is by providing coordinates as can be done using any spatial data representation in which geometry can be represented. If the location is a spatial thing with a name and an identifier, it can be referenced instead of having to provide its coordinates. There are many popular repositories containing sets of identifiers for Spatial Things such as Geonames, DBpedia, and Wikidata.

FeatureSpecification / GroupMaturityCurrent implementations
Select browsers…
Encoding any spatial dataThe GeoJSON FormatCandidate Recommendation
Geography Markup Language (GML) Encoding Standard
Open Geospatial Consortium Inc.
Recommendation
Geography Markup Language (GML) simple features profile (2.0)Recommendation
GeoSPARQL - A Geographic Query Language for RDF DataRecommendation
OGC GeoRSS Encoding StandardRecommendation
OGC KML 2.3Recommendation
Sensor descriptionSemantic Sensor Network Ontology
Spatial Data on the Web Working Group
Recommendation
Geographic information -- Observations and measurementsRecommendation
Temporal data representationTime Ontology in OWL
Spatial Data on the Web Working Group
Recommendation
Data cubesThe RDF Data Cube Vocabulary
Government Linked Data Working Group
Recommendation
Representation of geometryWell-known Text Representation for Geometry in OpenGIS Implementation Specification for Geographic information - Simple Feature AccessRecommendation
GeohashLiving Standard
Reference a location by nameGeoNamesLiving Standard
DBpediaLiving Standard
WikidataLiving Standard

Specifications in progress

The Web of Things Thing Description specification can be used for lightweight and common representation of 'Things' which are connected to the Web. It lets you describe their metadata and interfaces. The encoding is JSON-LD. The set of terms defined is small, but it is possible to re-use terms from other models such as schema.org or SOSA/SSN.

Not an established standard, but well known, the Schema.org vocabulary is being defined as an ongoing community activity and is used to add meaningful markup to web pages and email messages. It can be used with many different encodings including RDFa, Microdata and JSON-LD. The vocabulary defines relevant concepts for spatial data such as Place and Event.

FeatureSpecification / GroupMaturityCurrent implementations
Select browsers…
Description of Web-connected devicesWeb of Things (WoT) Thing Description
Web of Things Working Group
Candidate Recommendation
Encoding any geospatial dataSchema.orgLiving Standard

N/A

Exploratory work

CoverageJSON (CovJSON) is a data format for describing "coverage" data in JSON: many kinds of data whose properties vary with space, time and other dimensions, including (but not limited to) satellite imagery, weather forecasts and river gauge measurements.

CityJSON is a JSON-based format for encoding a subset of the CityGML data model, aimed at representing 3D models of cities and landscapes. A CityJSON file represents both the 3D geometry and the semantics of the city features of a given area, such as buildings, roads, rivers, the vegetation, and the city furniture.

The ISA Programme Location Core Vocabulary is a common RDF-based vocabulary to describe the address or location of a spatial thing. It defines a set of general terms for describing location information that can be extended based on domain-specific requirements and covers geographical names, geometries, and postal addresses.

The vCard Ontology is an RDF-based ontology for describing people and organizations. It includes terms for describing postal addresses and 0D geometries (points, WGS 84 only).

To partition RDF data for the web using spatial and/or temporal data elements, QB4ST: RDF Data Cube extensions for spatio-temporal components is available. The Note Publishing and Using Earth Observation Data with the RDF Data Cube and the Discrete Global Grid System offers guidance on using RDF Data Cubes on geospatial data.
FeatureSpecification / GroupImplementation intents
Select browsers…
Encoding coveragesThe CoverageJSON Format
Encoding data about citiesCityJSON
Encoding locationISA Programme Location Core Vocabulary
European Commission
Encoding location of people and organizationsvCard Ontology - for describing People and Organizations
Semantic Web Interest Group
Spatio-temporal data cubesQB4ST: RDF Data Cube extensions for spatio-temporal components
Spatial Data on the Web Working Group
Publishing and Using Earth Observation Data with the RDF Data Cube and the Discrete Global Grid System
Spatial Data on the Web Working Group

Features not covered by ongoing work

TopoJSON
A community-defined extension of GeoJSON which reduces redundancy in the description of a geometry, by splitting it into segments (referred to as "arcs") that can be re-used.

Features not fully reviewed

These features are established standards in the geospatial domain, and of possible interest to the Web community, but are not fully reviewed as to their compliance to modern Web architecture.

Timeseries
An OGC standard for describing measurements of the same thing that occur many times over time. There is a Timeseries Profile of Observations and Measurements and a TimeSeriesML XML encoding.
Moving features
An OGC standard for encoding representations of movement of geographic features. The primary use case is information exchange.

Discontinued features

Basic Geo
A basic RDF vocabulary for representing lat(itude), long(itude) and other information about spatially-located things, using WGS84 as a reference datum. It was designed as an exercise and has not had careful review.