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What Is Metadata?



Metadata or "data about data" describes the content, quality, condition, and other characteristics of data. The concept of metadata is familiar to most people who deal with geospatial data issues. A map legend is pure metadata. The legend contains information about the publisher of the map, the publication date, the type of map, a description of the map, geospatial references, the map's scale and its accuracy, among many other things. Metadata are simply descriptive information applied to a digital geospatial file. Metadata utilize a common set of terms and definitions to document geospatial data.

Metadata helps people who use geospatial data find the data they need and determine how best to use it. Metadata benefit the data producing organization as well. As personnel change in an organization, undocumented data may lose their value. Later workers may have little understanding of the contents and uses for a digital database and may find they can't trust results generated from these data. Lack of knowledge about other organizations' data can lead to duplication of effort. The generation of metadata is an essential element of building a digital map database.

The FGDC "Content Standard for Geospatial Metadata" was developed to effect a common set of terminology and definitions for the documentation of digital geospatial data. The standard establishes the names of data elements and compound elements (groups of data elements) to be used for these purposes, the definitions of these compound elements and data elements, and information about the values that are to be provided for the data elements. There are 334 different elements in the FGDC standard, 119 of which exist only to contain other elements. These compound elements are important because they describe the relationships among other elements.

Metadata consist of information that characterizes data. Metadata are used to provide documentation for data products. Metadata helps publicize and support the data an organization has produced. This information must be standardized in order to facilitate information sharing and automated storage and retrieval technology. Online systems for handling metadata need to rely on their being predictable in both form and content. Predictability is assured by conformance to standards. Metadata that conform to the FGDC standard are the basic product of the National Geospatial Data Clearinghouse, a distributed online catalog of digital spatial data.

The major uses of metadata are to:

Maintain an organization's internal investment in geospatial data
Provide information about an organization's data holdings to data catalogues, clearinghouses, and brokerages
Provide information needed to process and interpret data to be received through a transfer from an external source

The information included in the standard was selected based on four roles that metadata play :

Availability
Data needed to determine the sets of data that exist for a geographic location.

Fitness for use
Data needed to determine if a set of data meets a specific need.

Access
Data needed to acquire an identified set of data.

Transfer
Data needed to process and use a set of data.

These roles form a continuum in which a user cascades through a pyramid of choices to determine what data are available, to evaluate the fitness of the data for use, to access the data, and to transfer and process the data.

The exact order in which data elements are evaluated, and the relative importance of data elements, will not be the same for all users.

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