Another definition is "the technology, policies, standards, human resources, and related activities necessary to acquire, process, distribute, use, maintain, and preserve spatial data".
A further definition is given in Kuhn (2005):[3] "An SDI is a coordinated series of agreements on technology standards, institutional arrangements, and policies that enable the discovery and use of geospatial information by users and for purposes other than those it was created for."
The original example of an SDI is the United States National Spatial Data Infrastructure (NSDI), first mandated in the OMB Circular A-16 in 1996.
In Europe since 2007, INSPIRE is a European Commission initiative to build a European SDI beyond national boundaries; the United Nations Spatial Data Infrastructure (UNSDI) plans to do the same for over 30 UN Funds, Programs, Specialized Agencies and member countries.
It is not complete, is a sample of National Spatial Data Infrastructure (NSDI) official websites.