Meta-data is the mechanism that producers have that enables potential users to find, analyse and evaluate their resources (data sets and services) and determine their fitness for use
The term metadata and the metadata itself have become widely used over the last few years by the geo-community as if it was something new. In reality, however, its underlying concepts have been in use for generations. A map legend, for example, is one embodiment of metadata, containing details about the publisher of the map, its publication date, the type of map, the spatial reference and the map’s scale and accuracy, etc. This connection has become somewhat lost in the transition from analogue to digital data production processes. Some authors define three categories of metadata, based on how it is actually used: i.e. discovery, exploration and exploitation metadata. Discovery metadata simply enables users to find existing data and services. Discovery metadata helps answering the question “who has what data/service and from where?”, the where being an area of interest defined by means of coordinates, geographical names or administrative areas. Exploration metadata enable users to determine whether some existing data/service is useful for their application. Exploration metadata answer questions like “why, when and how was certain data collected”. Exploitation metadata enable users to access, transfer, load, interpret and use data/services in their applications. In addition to access, this type of metadata also includes details about the price of the data/service and licensing and copyrights. Metadata is defined as a formalized and agreed upon set of properties that describe in a significant amount of detail the characteristics of a data set and/or service. ISO has therefore specified in its 19100 suite of standards the set of properties that properly describe a data set and a service. The ISO 19115 standard defines the metadata for vector data sets. It is applicable to a whole data set, aggregations of data sets, individual features, and the various classes of objects that compose a feature. This standard defines a large set of metadata properties (400+), some of which are considered mandatory and some optional. To adhere to the standard, one should implement descriptions that incorporate the mandatory properties and a selection of the optional properties. The result is known as an ISO profile, a subset of the original standard. As mentioned earlier, metadata is mainly disseminated via metadata catalogues that meet the OGC-defined Catalogue Service Web (CSW)-implementation specification. This specification defines the interfaces and binding mechanisms required to publish and access digital catalogues of metadata for data, services, and related resources. Implementations of the CSW specification are known as Catalogue Services. A repository of CSW services is known as an OGC Catalogue.