What is SDI?
The emergence of spatial data infrastructures (SDIs) is closely associated with the efforts of collecting and producing geospatial data, as well as the advancement of surveying and computer technologies. In the past decades, a large amount of geospatial data, such as remote sensing images and GPS locations, have been collected by government agencies such as the U.S. Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA). Meanwhile, the fast development of geographic information systems facilitates the derivation of various data products from the collected data, such as topographic maps, land cover data, transportation networks, and hydrographic features. As location‐based services are becoming increasingly popular, vast amounts of volunteered geographic information (VGI) (Goodchild 2007) has also been contributed by the general public through smart mobile devices and social media platforms. In addition, the componentization of GIS brings geospatial services that provide data processing and spatial analysis functions in the general Web environment. The large number of geospatial data, services, maps, and others, however, do not ease the use of these geospatial resources. On one hand, it is challenging to find and access these digital resources which are widely distributed at different government agencies and websites (Li, Wang and Bhatia 2016). On the other hand, a lot of data redundancies exist, and money and human resources were wasted in duplicated data collection and maintenance efforts (Rajabifard and Williamson 2001, Maguire and Longley 2005). These problems were recognized by governments of the countries around the world, and many spatial data infrastructures were constructed since 1990s (Masser 1999). In the U.S., a national spatial data infrastructure (NSDI) initiative was started in 1993 to provide standardized access to geographic information resources (National Research Council 1993). An official definition of NSDI, according to the Executive Order 12906, is “the technology, policies, standards, and human resources necessary to acquire, process, store, distribute, and improve utilization of geospatial data.” The Federal Geographic Data Committee (FGDC) is charged with coordinating the efforts to develop the NSDI in the U.S. The naming also indicates that SDI is recognized as an infrastructure similar to other types of infrastructures, such as electricity grids and water supplies, and that it plays fundamental roles in the socioeconomic and environmental developments of a country. Three parallel fronts were developed in the NSDI program: 1) a set of data standards for formalizing data and metadata; 2) a clearinghouse network providing data storage and online access; and 3) a set of framework data for the entire country, such as administrative boundaries (Longley et al. 2001, Maguire and Longley 2005). Spatial data infrastructure presents a solution to the problems of resource discovery and data redundancy. It provides a unified platform where people can go and search geospatial data, maps, services, and other digital resources. As multiple government agencies are sharing their data on one platform, SDI reduces data redundancy and the extra efforts in collecting duplicated geospatial data. From a cost/benefit perspective, SDI allows geospatial data to be collected once and reused multiple times in different applications. More generally, SDI can be considered as an important element in the e‐government (Georgiadou, Rodriguez‐Pabón and Lance 2006) and open‐government movement to increase the transparency of governmental activities and to enhance public participation. Better access to geospatial data also stimulates the growth of new businesses which may not be possible otherwise (Ralston 2004).
Important Definitions
1. Spatial data infrastructure: The technology, policies, standards, and human resources necessary to acquire, process, store, distribute, and improve utilization of geospatial data, services, and other digital resources.
2. Geoportal: A gateway website through which people can search, discover, access, and visualize the geospatial resources within a SDI.
3. Metadata: Documentation about who, when, how, what, why, and many other facets of the data and the data production process. Metadata can be used for describing not only data, but also tools, services, and other geospatial resources.
4. Data standard: A commonly agreed specification on how data should be recorded and described.
5. Geospatial interoperability: The ability of different geographic information systems to share, exchange, and operate (heterogenous) geospatial data and functions.
6. Web service: A Web application that provides standardized application programming interfaces to allow remote access to data and functions over the Internet.
Key Components of a SDI
A SDI consists of many components. In addition to the digital geospatial resources, a SDI also needs hardware, software, people, organizations, standards, policies, and many others to function properly. Constructing a SDI also needs effective communications between communities, and negotiations among organizations and even countries to reach agreements. While a SDI has many components, this chapter will particularly focus on geoportals, metadata, and search functions, which are three key components of a typical SDI.

Geoportals are Web gateways that provide one‐stop access to geospatial resources (Tait 2005). Geoportals are probably the most visible part of SDIs, since they are the main interfaces through which people can search and find geospatial resources. Geoportals are typically developed using Web‐based technologies and off‐the‐shelf GIS software packages. A database management system (DBMS) is used to store and manage the metadata of the geospatial resources contained in the SDI. A Web interface, which often contains a map, enables end users to interact with the system and to conduct searches. When a search is performed, a HTTP (Hypertext Transmission Protocol) request will be sent to the Web server which hosts the geoportal. After querying the metadata stored in the database, the geoportal will then send back the result to the client through a HTTP response. Geoportals are typically designed to be used by both GIS professionals and the general public. One important function of geoportals is helping users discover the existing geospatial resources. This resource discovery process often follows the publish‐find‐bind pattern (Rose 2004, Maguire and Longley 2005), in which:

1) providers publish the metadata of their data and services to ageoportal;
2) users perform a search on the geoportal and potentially find the data;
3) users consume the data and services from the providers. Figure 2 illustrates these three steps.

Metadata provide documentations on the content and the production process of geospatial resources. Metadata are often called the data about data, and include information such as titles, descriptions, data categories, the locations and time of the data collection, the data collectors, the used coordinate systems and map projections, and the data cleaning and processing procedures. Metadata can also be used for describing geospatial services by providing information about the data and functions offered by the services, the input and output, the developers, the development time, and others. In short, metadata are about all aspects of digital geospatial resources. Metadata are fundamentally important for SDIs. When data and services leave their original data production context and are integrated into a SDI, metadata provide the primary information based on which GIS users can understand and use digital geospatial resources. Without metadata or with only poorly constructed metadata, it is very difficult, if not impossible, for data and services to be reused. The quality of metadata also determines the result of resource discovery. Many geoportals rank the relevance of geospatial resources to user queries based on the information contained in their metadata. Complete and accurate metadata allow geoportals to find and rank geospatial resources based on locations, time, thematic attributes, data types, published years, data collectors, and many other conditions explicitly or implicitly specified in the user queries. To ensure the quality of metadata, standards are established to define the necessary elements that should be included in metadata. In the U.S., the FGDC is responsible for coordinating the development of metadata standards, and its Content Standard for Digital Geospatial Metadata (CSDGM) has been used by many U.S. government agencies to formalize metadata. Since 2010, FGDC has endorsed a series of international metadata standards (e.g., the ISO 191** standards) to promote Global Spatial Data Infrastructure (GSDI).
GISFY team has built SDI framework and deployed at (MNR) Ministry of Natural Resources, Belize.
Funding Agency: Belize Social Investment Fund
URL :https://portal.bnsdi.gov.bz/