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.
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.
| Feature | Specification / Group | Maturity | Current implementationsSelect browsers… |
|---|---|---|---|
| Encoding any spatial data | The GeoJSON Format |  | |
| Geography Markup Language (GML) Encoding Standard Open Geospatial Consortium Inc. |  | ||
| Geography Markup Language (GML) simple features profile (2.0) | | ||
| GeoSPARQL - A Geographic Query Language for RDF Data | | ||
| OGC GeoRSS Encoding Standard | | ||
| OGC KML 2.3 | | ||
| Sensor description | Semantic Sensor Network Ontology Spatial Data on the Web Working Group | | |
| Geographic information -- Observations and measurements | | ||
| Temporal data representation | Time Ontology in OWL Spatial Data on the Web Working Group | | |
| Data cubes | The RDF Data Cube Vocabulary Government Linked Data Working Group | | |
| Representation of geometry | Well-known Text Representation for Geometry in OpenGIS Implementation Specification for Geographic information - Simple Feature Access | | |
| Geohash |  | ||
| Reference a location by name | GeoNames | | |
| DBpedia | | ||
| Wikidata | |
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.
| Feature | Specification / Group | Maturity | Current implementationsSelect browsers… |
|---|---|---|---|
| Description of Web-connected devices | Web of Things (WoT) Thing Description Web of Things Working Group | | |
| Encoding any geospatial data | Schema.org | | 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).
| Feature | Specification / Group | Implementation intentsSelect browsers… |
|---|---|---|
| Encoding coverages | The CoverageJSON Format | |
| Encoding data about cities | CityJSON | |
| Encoding location | ISA Programme Location Core Vocabulary European Commission | |
| Encoding location of people and organizations | vCard Ontology - for describing People and Organizations Semantic Web Interest Group | |
| Spatio-temporal data cubes | QB4ST: 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.