International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
recognition that the data layers and tables in most GIS 
implementations come from multiple organizations. An 
organization typically develops some, but not all, of its own 
spatial data content. At least some of the layers will be from 
external sources. Thus GIS data management, by its very 
nature, is distributed among many users (ESRI. March 2003). 
GIS requires a distributed information system concept to 
manage and share spatial data. Because GIS users are hungry 
for quality geographic information, there is a fundamental 
need for users to share their data. Today, thousands of 
organizations worldwide invest billions of dollars annually 
automating and integrating map information for their focused 
GIS projects. Their need for up-to-date geographic 
information drives these efforts. SDI has become an essential 
2. Information Modeling for Spatial Data Infrastructure 
A Spatial Data Infrastructure interconnects GIS nodes across 
the World Wide Web to promote information sharing and 
access. The SDI concept binds many GIS nodes into loosely 
  
  
Figure 1 : Building Blocks of SDI 
In practice, each node in an SDI would be built to provide 
one or more of these three capabilities. For example, a city 
might provide a catalog referencing the available data and 
services at its Web site along with a series of data and 
mapping services. A small GIS shop would be able to access 
and use those services in their Software seat across the 
Internet. In another case, a state government might provide 
the metadata catalog describing its services as well as data 
and services at other GIS portals within the state. The state 
might also publish GIS Web services with a set of HTML 
clients to access various Internet map and data services. At 
its most basic level, a Spatial Data Infrastructure is realized 
through a catalog holding metadata about available data and 
services. As the number of participating organizations and 
users grow, so will the numbers of entries and complexity of 
the metadata catalog. The role of a metadata server and 
search tools becomes more critical. Metadata server makes 
accessing and managing geographic data simple. 
3. Building National and Global Data Models for 
SDI 
  
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tool when information integration is critical. It works with 
geographic information from many sources to support a 
broad range of applications. SDI can repurpose information 
for new applications that go beyond the data's original intent. 
For example, information compiled for land records 
management can be used for environmental applications, 
utilities, emergency response, homeland security, and many 
other applications. Spatial data management includes not 
only data collection but also data dissemination. 
Interoperability enables data sharing between organizations 
and across applications and industries, which results in the 
generation and sharing of more useful information. 
coupled information networks. There are three functional 
node in information model of SDI. 
GIS Users—-A wide range of users who connect to the 
catalogs, search for useful geographic information, and then 
connect to GIS portals that provide the information access. 
GIS Users can find the data they need, quickly review and 
display its contents, and read or create metadata. GIS Users 
can also manage spatial data stored in folders on local disks 
or in relational databases that are available on their network. 
Metadata Catalogs--A series of well-organized catalogs that 
describe and reference geographic information sets at each 
node. Metadata is information about GIS data describing a 
collection of data. Metadata for geographical data may 
include the source of the data, its creation date and format, 
its projection, scale, resolution, and accuracy, and its 
reliability with regard to some standard. 
GIS Portal--A GIS portal that provides access to FTP 
download sites, maps, reports, Internet GIS services, and so 
on. GIS Portal publishes GIS Data & Services & 
Documents. A broad range of GIS users access metadata 
and services with any client (wireless, html, java,pocket PC, 
windows). 
GIS professionals are learning about the benefits of a Spatial 
Data Infrastructure (SDI). The SDI, developed by national, 
state, and local governments, promotes the vision of a 
framework for GIS users to openly share geographic 
information with one another. The SDI is meant to address 
the needs for users to interconnect their existing GIS nodes 
across the Internet (and in many cases over secure networks) 
in order to share information with one another openly (i.e., 
based on standards). Many people are familiar with the term 
NSDI, or National Spatial Data Infrastructure, a concept 
defined as the technologies, policies, and people necessary to 
promote the sharing of geospatial data throughout all levels 
of government, the private and nonprofit sectors, and the 
academic community. Recent discussions have revolved 
around the GSDI, or Global Spatial Data Infrastructure, 
which describes a framework for data sharing at the global 
level. Many GIS users want to provide information portals to 
publish a metadata catalog for their collection of GIS data 
and services. A few clearinghouse sites want to provide a 
catalog of information sets published by many users. 
Sometimes the data and services will be published for a user's 
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