(1) Difference between measured quantities and "true" or accepted values and how these values were arrived at. (2) Validity of data measured with respect to an independent source of higher reliability and precision. See the topic on Data Quality for a more detailed discussion.

Generation of geographic coordinate locations based on addresses. For example, a data file containing student addresses can be matched to a street coverage that contains addresses creating a point coverage of where the students live. See the topics on Data types and Data creation/automation for more details.

A catalog or index, usually provided on-line, for browsing and/or searching for databases or datasets. Metadata, or information about the data, is used to catalog and describe the available datasets. See the topic on Clearinghouse concepts for more details.

Since 1994, this has been the federally-endorsed content standard for entering metadata for geospatial data in the United States of America. This standard was developed specifically for geospatial data, though it has been used for non-spatial data as well. In its generic form, it is fairly flexible for describing different types of data, but there are several profiles or modifications of this standard which are more appropriate for specific types of data. The CSDGM is only one of many standards developed and approved by the Federal Geographic Data Committee. See the topic on Overview of the metadata content standard for more details.

A reference system used to locate features on the earth's surface. Two basic types:

(1) A catalog of all of the attributes for a data set, along with all of the constraints placed upon the attribute values during the data definition phase. Can include the range and type of values, category lists, legal and missing values, and the legal width of the field. (2) The part of a database containing information about the files, records, and attributes rather than just the data. See the topic on Database principles for more details.

Different levels of data collections. Typically ranges from data series, dataset to individual data features. For instance, a digital topographic map is available for each 7.5 minute quadrangle in the U.S. Is each quadrangle considered a single data set, or is the entire collection a data set? Determining at what level of granularity to require metadata may be difficult. For instance the only difference in the 7.5 minute topographic maps is the area they cover, and sometimes variations in their projection/datum parameters. Do you create a unique metadata document for each, or just one metadata document that references a database that contains the actual variations? See the topic on Using and Implementing Metadata for more details.

(1) The result of the conceptual design process. A generalized, user-defined view of the data related to applications. (2)The logical means of organization of data for use in an information system, including vector and raster formats. See the topic on Data models for more details.

A named collection of logically related data items arranged in a prescribed manner. There may be different levels or granularity associated with data sets.

One of the seven main sections of the FGDC's Content Standard for Digital Geospatial Metadata (CSDGM), providing information on the dataset's sources, processes, positional and attribute (thematic) accuracy. See the topic on Data Quality for more details.

A set of parameters and control points used to accurately define the three-dimensional shape of the Earth (e.g., as a spheroid). The datum is the basis for a planar coordinate system. For example, the North American Datum for 1983 (NAD83) is the datum for map projections and coordinates within the United States and throughout North America.

A system or network of systems and services designed to deal with ill-structured or semi-structured problems, where criteria for making decisions is difficult to define. One commonly defining criteria for a decision support system is the means for generating a series of decision alternatives for comparison and evaluation. See the topic on Decision making for more details.

One of the seven main sections of the FGDC's Content Standard for Digital Geospatial Metadata (CSDGM), providing information on where and how to obtain a dataset and what format(s) it is made available in. See the topic on Data Sources for more details or the topic Good and bad examples of metadata for specific examples.

An attribute will have a specific type of domain of categories associated with it. Four types of domains are recognized within the metadata content standard (CSDGM):

A type of metadata standard widely implemented on the World Wide Web that is specifically intended to support electronic resource discovery, of which geospatial data is only one component. See the topic, Overview of the metadata content standard for a discussion of different standards including the Dublin Core and the ISO standard.

A spatial phenomenon of a defined type that has at least one key attribute value different from the corresponding attribute values of surrounding phenomena. Simple datasets may be composed of only one entity, for instance "roads", "elevation", "soils". A single dataset can also be composed of more than one entity. For instance, a dataset representing boundaries may contain two entities representing land ownership and land management. Some pieces of land may have a distinct ownership, but portions of the land having some of the same boundaries in common may be managed differently. See the topic on Database principles for more details.

One of the seven main sections of the FGDC's Content Standard for Digital Geospatial Metadata (CSDGM), the Entity and Attribute Information section provides information about the dataset that is roughly equivalent to a data dictionary, including a description of the structure and content of the database including its entities, attributes, attribute domains, and relationships between different entities and attributes. See the topic on Database principles for more details or the topic on Good and bad examples of metadata for specific examples.

Attributes which are defined to keep track information specific to attributes such as when they were entered, updated, by whom, by what method, quality of method, etc. See the topics on Database principles for more information and a sample exercise.

An interagency committee, organized in 1990, that promotes the coordinated use, sharing, and dissemination of geospatial data on a national basis. The FGDC is composed of representatives from seventeen federal agencies, and is responsible for coordinating the development of the National Spatial Data Infrastructure (NSDI).

Evaluation of a dataset to determine whether it meets certain criteria (area, scale, quality, time period, spatial organization/format, attributes) necessary in order for it to be used on its own or integrated with other datasets for purposes of management and analysis. Metadata is critical for determining data's fitness-for-use, since without this documentation, the time required to find, obtain, import, explore and test each potential dataset to determine its fitness-for-use would be prohibitive.

Conversion of locations in geographic space into computer readable form. This usually means making a digital record of the point's coordinates. Though geocoding refers to the generic process of converting analog data into digital geospatial data, sometimes it is used to refer to the process of address-matching. See the topic on Data creation/automation for more details.

The process of moving from one map scale to a smaller (less detailed) scale and changing the form of features by simplification, etc. A description of the generalization associated with a dataset is an important component for understanding the dataset's quality and fitness-for-use.

One of the seven main sections of the FGDC's Content Standard for Digital Geospatial Metadata (CSDGM), providing a description, purpose, and creator/publisher of the dataset, as well as information on the area and time period it covers. See the topic on Good and bad examples of metadata for examples.

A worldwide federation of national standards bodies (e.g., ANSI from the U.S.) that develops international standards. A Technical Committee (ISO/TC211) is developing international Geographic Information/Geomatics standards including a standard for geospatial metadata. See the topic Overview of the metadata content standard for a discussion of different metadata standards.

The extent to which users, software and data can move between computer environments without change or retraining. Standards such as the Spatial Data Transfer Standard (SDTS) and the Open Geodata Interoperability Specification (OGIS) have been developed to increase interoperability in the area of data transfer and use. See the topic on Interoperability/standards for more information on this subject.

A narrative of source materials used and procedures used to produce the product as well as a record of updates/changes. One component of the Data Quality Information Section of the metadata content standard; see the topic on Data Quality for more details.

A description of the fidelity of relationships encoded in the data structure, such as permissible values, and topological requirements. One component of the Data Quality Information Section of the metadata content standard; see the topic on Data Quality for more details.

The reduction needed to display a representation of the Earth's surface on a map. A statement of a measure on the map and the equivalent measure on the Earth's surface, often expressed as a representative fraction of distance, such as 1:24,000 (one unit of distance on the map represents 24,000 of the same units of distance on the Earth). See the topic on Projections and Scale for more details on map scale, which is also an important element in deterring data's fitness-for-use.

A mathematical model that transforms the locations of features on the Earth's surface to locations on a two-dimensional surface. Because the Earth is three-dimensional, some method must be used to depict a map in two dimensions. Some projections preserve shape; others preserve accuracy of area, distance, or direction. Map projections project the Earth's surface onto a flat plane. However, any such representation distorts some parameter of the Earth's surface be it distance, area, shape, or direction. See the topic on Projections and Scale for issues related to projections.

A distributed network of geospatial data producers, mangers and users linked electronically. The Federal Geographic Data Committee (FGDC) has developed resources to help governmental, non-profit, and commercial participants to make their collections of spatial information searchable and accessible on the Internet through a formal clearinghouse, using established standards for metadata and search/query protocol.

A specific World Wide Web-based clearinghouse that serves as a cross-reference point for the distributed database of all U.S. government public domain and other geographic information. Organized by the Federal Geographic Data Committee (FGDC). See the topic on Clearinghouse concepts for more details.

Computer programming languages and data bases that support "objects." Objects are standard "classes" that contain all of the properties of an object. As a simple example, an object class could be a point, that will contain the latitude and longitude of the point, a feature code for the point, any necessary text describing the object, and any special behaviors or relationships assigned to that point. Classes are hierarchical, with super-classes and sub-classes. Classes and sub-classes of objects inherit the properties of their super-class. See the topic on Database principles for how metadata relates to object-oriented and relational databases.

A geospatial data standard that allows for interoperability of data software formats, developed by the Open GIS Consortium (OGC). See the topic on Interoperability / Standards for more details.

Refers to the number of significant digits used to store numbers, and in particular, coordinate values. Precision is important for accurate feature representation or exactness. Precision can also apply the exactness of attribute or thematic description (e.g. how precisely is a road described? "Highway" vs. "Four-lane, divided, limited access asphalt-base highway, last maintenance January 1990". Precision is an important component of the Data quality description for a dataset.

Metadata may be used to document data, and it may also be used to document processes. For instance, several individual datasets may be combined in a GIS analysis process to produce a "factor map" or a map to indicate locations of suitability based on different factors. Not only is it important to document the individual sources used to create this suitability map, but it is also important to document the process taken to arrive at the final map. Documentation of this sort is important to uphold decisions (see the topic on Decision making for more details.)

Part of a dataset's lineage or pedigree, describing how the data was created and formatted. One component of the Data Quality Information Section of the metadata content standard; see the topic on Data Quality for more details.

A modification to an existing standard (either by addition or by simplification) to better describe a specific sub-set of information. The Spatial Data Transfer Standard (SDTS) has two profiles, one for vector data and one for raster data. Profiles of the metadata content standard (CSDGM) are currently under development for cadastral data, wetlands, digital orthoimagery, soils, vegetation, and biological data.

A data model and data structure that represents features or continuous fields as a series of grid cells with individual values.

A data model based on multiple flat files for records, with dissimilar attribute structures, connected by a common key attribute. Most GIS datasets use a relational database to link attribute information to spatial information.

Accuracy at which a given map scale can depict the location and shape of geographic features. The larger the map scale, the higher the possible resolution. As map scale decreases, resolution diminishes and feature boundaries must be smoothed, simplified, or not shown at all. For example, small areas may have to be represented as points. See the topic on Projections and Scale for more details on the relationship between resolution and scale, which are important in evaluating a dataset's fitness-for-use.

The formal standard specifying the organization and mechanism for the transfer of GIS data between dissimilar computer systems. Adopted as FIPS 173 in 1992, SDTS specifies terminology, features types, and accuracy specifications, as well as a formal file transfer method for any generic geographic data. Subsets for the standard for specific types of data, vector and raster for example, are called profiles. For more information see the topic on Interoperability / Standards.

One of the seven main sections of the FGDC's Content Standard for Digital Geospatial Metadata (CSDGM), providing information on a dataset's internal structure (type of data model, number and type of components, type of topological relationship encoded). See the topic on Data models for more information or Good and bad examples of metadata for specific examples.

One of the seven main sections of the FGDC's Content Standard for Digital Geospatial Metadata (CSDGM), providing information on how the dataset is referenced to the earth's surface, either by a type of coordinate system, or some other system such as legal description or address. See the topic Good and bad examples of metadata for specific examples.

A coordinate system common in utility and surveying applications in the lower 48 United States and based on zones drawn state by state on Transverse Mercator and Lambert Conformal Conic projections.

The spatial relationships between connecting or adjacent coverage features (e.g., lines, nodes, polygons, and points). Topological relationships are built from simple elements into complex elements: points (simplest elements), lines (sets of connected points), areas (sets of connected lines). Redundant data are eliminated because an line may represent a linear feature, part of the boundary of an area feature, or both. Topology is useful in GIS because many spatial modeling operations don't require coordinates, only topological information.

A data model structure using node and connecting segments as the basic building block for representing coordinate-based geographic features of a geometric nature (points, lines, and polygons). See the topic on Data models for more details.

World Geodetic Reference System of 1984. A higher precision version of the GRS80 used by the United States Defense Mapping Agency in world mapping. A common datum and reference ellipsoid for hand-held GPS receivers.