Spatial Data Infrastructure (SDI)

The interoperability between different systems is now a necessity in any engineering project. In the field of Geographic Information Systems, interoperability has been achieved through the standards developed by the Open Geospatial Consortium (OGC). This organization, made up of companies, universities and the civil service has developed quite a series of protocols and standards over the last few years which provide the technological framework needed to achieve this interoperability.

Spatial Data Infrastructures (SDIs) are technology suites, but are also, and above all, a group of policies and institutional agreements to ensure that geographical information can be discovered and spread with no technical impediments. This is why initiatives like the American NSDI, INSPIRE in Europe or IDEE in Spain emerged to try to homogenize the discovery of and access to the information produced by the numerous civil services.

SDIs are therefore configured as authentic networks of systems that publish geographical information in very different forms but always following the same set of standards, permitting the integration of information from multiple origins into web visualization systems known as geoportals. A geoportal is a web application used to find information by accessing metadata servers, and visualize it on the web itself using protocols geared towards this end.

OGC standards

The OGC standards have brought interoperability to a field in which each technological supplier was offering their own access interface to the publication of cartography, causing what is known as vendor lock-in. By means of the different standards which are mentioned below, the application which produces the information from the clients that use it can be uncoupled, thus multiplying the applications and the possibilities of utilizing this information in all types of systems, whether they belong to a Spatial Data Infrastructure or not.

Catalogue Service

The catalogue service standardizes the way in which the metadata of all types of geographical information is published, both that which is published through other standards as well as any type of geographical resource (scanned photographs, printed maps, etc.). This service is the key component in an SDI to be able to offer users the possibility of finding out what information the different participants publish: companies and above all the civil service .

Go to the OGC page about catalogue service

Web Map Service

Its object is to be able to visualize Geographical Information. It provides a representation, an image from the real world of a required area. This representation can come from a data file from a GIS, a digital map, an orthophoto, a satellite image,…It is organized in one or more layers, which can be visualized or concealed one by one. Certain available information can be consulted, as well as the characteristics of the image of the map.

This OGC specification allows raster and vector data to be visually overlayed, in a different format; with a different Reference System and Coordinates System and in different servers, whereby a rasterized image in a widely used format such as PNG, JPG or GIF is always sent back to the end user.

Go to the OGC page about WMS

Web Feature Service

Allows access to, and the consultation of, all the attributes of a spatial element, such as a river, a street or a city, represented in vector mode, with a geometry described by a set of coordinates. The data provided is normally in GML format (another OGC standard). A WFS does not only allow the visualization of the information like a WMS, but the information can also be consulted and freely downloaded.

Go to the OGC page about WFS

Web Coverage Service

This service allows access to raster data without post-processing. That is to say, it allows access to real data in compressed or uncompressed format and single-band or multispectral. In this way it is possible to publish digital terrain models (DTM) or satellite images by means of standards.

 Go to the OGC page about WCS

Other standards [+]

In addition to the preceding standards, the OGC also has other lower level standards that are usually used in one way or another for the systems that they publish by means of the abovementioned standards.

Geography Markup Language

XML markup language to represent geometries and their attributes.

Coordinate Transformation Service

A standardized service for the transformation of coordinates between different reference systems and coordinate systems.

Filter Encoding

A standard to define filter expressions. For example, it is useful for filtering responses to requests for geometries from a WFS service.

Keyhole Markup Language

This recent standard is aimed towards the presentation of geographical information in interactive environments.

Styled Layer Descriptor

This standard permits the expression of symbologies in vector layers. By means of this standard, for example, the symbology of a WMS service can be defined dynamically.

Web Processing Service

By means of the definition of this service, geospatial analysis (traditionally on the desktop) is brought to the web.