M@IN - Accessing Spatial Data Tutorial


National Spatial Data Infrastructure - Clearinghouses

The National Spatial Data Infrastructure (NSDI) is an on-going effort to foster more efficient use, management, and production of spatial data.

The NSDI is a cooperative effort involving federal, state, and local government, the private sector, and academia. The vision, goals, and key components of the NSDI were set forth earlier in this guide.

The physical embodiment of the NSDI is the:

National Geospatial Data Clearinghouse

What is a clearinghouse, or more specifically, the National Geospatial Data Clearinghouse? The clearinghouse, which provides the means to search, query, and find geographic data, is the link between spatial data users and spatial data providers. The clearinghouse is a distributed, electronically connected network of spatial data producers, managers, and users.

The clearinghouse is not a central repository where data sets are stored, but rather a comprehensive listing of data being produced by government agencies, universities, utilities, and many other organizations around the country. The clearinghouse allows users to determine what spatial data exist, find the data they need, evaluate the usefulness of the data for their applications, and determine how to obtain the data.

The data listing is augmented by a structured summary of information about the data or metadata.


Metadata, sometimes called "data about data", describe the content, quality, condition, and other characteristics of data. It is through the evaluation of the metadata that a user can determine if the data meets the user's needs. Metadata describe different aspects of data, including:

Identification -- What is the name of the data set? who developed the data set? What geographic area does it cover? What themes of information does it include? How current are the data? Are there restrictions on accessing or using the data?

Data Quality -- How good are the data? Is information available that allows a user to decide if the data are suitable for his or her purpose? What is the positional and attribute accuracy? Are the data complete? Were the consistency of the data verified?

Entity and Attribute Information -- What geographic information (roads, houses, elevation, temperature, etc.) is included? How is the information encoded? Were codes used? What do the codes mean?

Distribution -- From whom can I obtain the data? What formats are available? What media are available? Are the data available online? What is the price of the data?

By accessing a clearinghouse of spatial data, the user can resolve the dilemna posed earlier:

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