  Spatial data infrastructure (SDI) is the infrastructure that facilitates the
discovery, access, management, distribution, reuse, and preservation of digital
geospatial resources. These resources may include maps, data, geospatial
services, and tools. As cyberinfrastructures, SDIs are similar to other
infrastructures, such as water supplies and transportation networks, since they
play fundamental roles in many aspects of the society. These roles have become
even more significant in today's big data age, when a large volume of
geospatial data and Web services are available. From a technological
perspective, SDIs mainly consist of data, hardware, and software. However, a
truly functional SDI also needs the efforts of people, supports from
organizations, government policies, data and software standards, and many
others. In this chapter, we will present the concepts and values of SDIs, as
well as a brief history of SDI development in the U.S. We will also discuss the
components of a typical SDI, and will specifically focus on three key
components: geoportals, metadata, and search functions. Examples of the
existing SDI implementations will also be discussed.
