A Spatial Data Infrastructure can be defined as the collection of technological and non-technological components to facilitate and coordinate the exchange of and sharing of spatial data. The concept infrastructure is used to promote the concept of a reliable, supporting environment, analogous to a road or telecommunications network, that facilitates the access to spatial data. Data, metadata, access networks, standards, coordination, policies, funding, people and institutional frameworks are often considered among the key components of an SDI.
Spatial data infrastructures often are defined and described as a complex and dynamic phenomenon. Among the main reasons for the complex character of these infrastructures are the many components a spatial data infrastructure consists of, the diversity of involved stakeholders, and the many different objectives and ambitions of these stakeholders. Technological advancements, such as the emergence of web 2.0 technologies, and societal changes, such as the increasing use of geographic information in everyday life, are often mentioned as important drivers behind the dynamic character of spatial data infrastructures.
A key characteristic of spatial data infrastructures is the involvement of a large and diverse group of actors. Governments are often considered as the central actors in the development and implementation of spatial data infrastructure, since they are the major producers and users of geographic information. Governments at different administrative levels and in different thematic domains are involved in the creation, management, use and sharing of geographic data. But also private companies, non-profit organisations, research and education institutions and even citizens can participate in the development and implementation of a spatial data infrastructure. It is increasingly being argued that the involvement and engagement of each of these stakeholders group is essential to the realization of a successful spatial data infrastructure.
SDIs have been developed in many countries worldwide at local, national and international levels. Often a distinction is made between a between the first generation SDIs that have data as their key driver and are based on a product model and second generation SDIs in which user needs are the key driver and that are based on a process or development model. The latest generations of SDI strongly focus on the inclusion and engagement of non-government actors and organizations in the development and implementation of the SDI. Although SDI are by default distributed systems, involving many organisations, some SDI might be developed rather in an hierarchical way, while others are following a networked approach.