A Spatial Data Infrastructure (SDI) is “a framework of spatial data, metadata, users and tools that are interactively connected in order to use spatial data in an efficient and flexible way”( http://en.wikipedia.org/wiki/Spatial_data_infrastructure).
In the last decade, SDI has become the global trend in the Geographic Information Science (GIS) industry. Increasing spatial data and service sharing is motivated by (i) cost savings on data collection, maintenance and software; (ii) improved spatial data usability and consistency; and (iii) enhanced inter-organisational relationships and the best use of scarce GIS resources.
A SDI facilitates spatial data sharing and can be built with advanced relevant technologies and a set of standards, specifications and policies. The key point of a SDI is interoperability and integration that enables users from different areas such as government, the private sector and the general public to discover and access spatial data and services provided by different organisations.
Examples of SDI include INSPIRE (http://inspire.jrc.ec.europa.eu/index.cfm/pageid/48) in Europe, the National Spatial Data Infrastructure (NSDI) in the United State (http://www.fgdc.gov/nsdi/nsdi.html) and the Australia Spatial Data Infrastructure (ASDI) in Australia and New Zealand (http://www.anzlic.org.au/infrastructure_ASDI.html).