Components of an SDI
Geographical Data
According to Spanish legislation (LISIGE), geographical data are any data that, directly or indirectly, refer to a specific location or geographical area.
Geographical data and datasets must be in an electronic format and refer to the area of operation of the SDI, in this case, the municipality of Barcelona.
Geographical data can be “Base or Reference Data” or “Thematic Data”:
Reference Data
Essential georeferenced data that serve as a basis for constructing or referencing any other essential or thematic data. They are the reference geographical information used as a common base that allows for the overlay and integration of various types of thematic data.
Thematic Data
Data specific to applications or areas that use geographical information for a particular purpose. They include qualitative and quantitative values corresponding to attributes associated with the reference data (e.g. public facilities, protected areas, urban planning information).
Metadata
Metadata inform users about the characteristics of data, enabling them to understand their origin and purpose, to find and select the data of interest, and to use them effectively. The information contained in the metadata, therefore, refers to data quality, content, coverage, the spatial reference system, origin, purpose, distribution, legal restrictions, and update frequency.
The structure and content of metadata are based on the ISO 19115 standard, which provides procedures for describing geographical information sets from which profiles can be developed. Creating an accepted set of definitions and terminology facilitates the organisation and maintenance of data, as well as access and exchange between organisations, thereby promoting the appropriate use of information.
The European INSPIRE Directive requires a minimum number of mandatory fields for geographical information sets, which define their profile. It also classifies the different sets of geographical information into themes (addresses, cadastral parcels, administrative units, transport networks, etc.) and imposes the necessary regulations to ensure interoperability.
Services
A set of standardised geospatial services (OGC) offered to information systems accessible via the internet. The main services are as follows:
Map Service: WMS (Web Map Service) and WMTS (Web Map Tile Service)
The WMS allows the generation and distribution of dynamic maps over the internet through HTTP/HTTPS requests generated from spatial data, which can be viewed in web browsers or compatible GIS applications. These images or maps can contain multiple layers of graphical information and element attributes.
The WMTS, or tiled map service, like the WMS, provides a digital image from geographical data but significantly increases response speed by using collections of pre-generated tiles or parts of images at defined scale intervals.
Web Feature Service (WFS)
A WFS allows vector data and associated alphanumeric information to be queried and retrieved. It also allows spatial and alphanumeric queries and geometry manipulation (WFS-T).
Geolocation Service
This service allows for obtaining the coordinates of postal addresses, street intersections, or facilities, as well as the nearest postal address to a specific coordinate (reverse geolocation).
Catalogue Service for the Web (CSW)
This service allows users to discover, search, query and access geospatial information and data stored in catalogues distributed over the internet. CSW services are essential for data interoperability in SDIs, facilitating access to and integrating geospatial resources from different sources.
