The vision of “created once, used many times” has been spread out across the globe through the development of geospatial data infrastructure (GDI) initiatives, including their geoportals. Within the GDI, a geoportal facilitates discovery of and access to geospatial data. This chapter discusses some key considerations for the success of a geoportal in facilitating users to exploit the GDI potentials. The top priority is to offer a usable interface that facilitates visual thinking when users search and browse metadata items. Advanced support to enable geospatial and non geospatial web content integration and to advance group work activities through the geoportal are also considered of high importance.
2. Geoportals: Making Data Discoverable And Accessible
Geoportals are primarily concerned with providing catalog services (Maguire & Longley, 2005). In this regard, geo information users might have been familiar with some web catalog years before the rising of the GDI, where they could search for products of earth observations and satellite images through the web sites of specific data providers. In the GDI context, geoportals are functioned not only to publish products (i.e., resources) related to one specific provider, but to publish resources offered by various providers participating in the infrastructure, and to facilitate discovery of and access to the resources. As resources and providers can be very diverse in their content and level of authority, geoportals can therefore be classified as: (a) national or regional geoportals, such as the U.S. Geospatial One Stop – GOS1, GeoConnections2, Inspire Geoportal3 and (b) thematic geoportals, such as Food and Agriculture Organization (FAO) portal4, the European Protected Areas portal (Nature GIS)5, or Earth-Sun system gateway6.
Catalog services facilitate the publication and discovery of collections of geospatial resources, which are mostly offline and online data services. For publishing data, the data providers need to create metadata describing the data and, afterwards, publish them through the catalog client. This registering process can be done either by manual inputs or metadata harvesting. The metadata to be published should be encoded as a specific standard-conformant metadata (e.g., using ISO 19115 standard). For data discovery, the catalog services are equipped with tools to query and present metadata records as users initiate searches for data or required services (see Figure 1). The OGC specification for Catalog Services for the Web (CSW 2.0) defines the framework, interfaces, and bindings required for providing catalog services to geospatial community. Currently, several solutions of catalog services based on the CSW 2.0 specification are available (see e.g., Red Spider7, Terra Catalog8, GeoNetwork9).
Key Terms in this Chapter
Web Feature Services (WFS): OGC Specification that supports INSERT, UPDATE, DELETE, QUERY and DISCOVERY of geospatial features. A WFS outputs GML (Geography Markup Language) representation in response to queries from clients. A WFS-T (“WFS-Transactional”) is a WFS that supports transactions - add, delete, or update features.
GeoRSS: Geographically Encoded Objects for RSS feeds. RSS is a format for syndicating news and the content of web contents.
RDF/XML: An XML (eXtensible Markup Language) syntax for RDF (World Wide Web Consortium specification for Resources Description Framework)
Web Processing Services (WPS): They provide access to pre-programmed calculations and/or computation models that operate on spatially referenced data.
Web Mapping Services (WMS): OGC Specification that standardizes the way the clients request maps of georeferenced data in terms of named layers and parameters such as the size of the returned map.
Sensor Web Enablement (SWE): OGC initiative to standardize supporting linking of Sensor Collection Service (SCS) servers that gather readings from in-situ environmental sensors via a private network (cellular, microwave, etc.), and provides summaries or interpretations of those readings over the Web.
Styled Layer Descriptors (SLD): A map-styling language for producing georeferenced maps with user-defined styling.
ISO19115: Geographic Information – Metadata. International Organization for Standardization (ISO) 19115:2003 defines the schema required for describing geographic information and services.