Terms & Definitions

A

ABSCISSA:

The coordinate of a point in a plane cartesian coordinate system obtained by measuring parallel to the x-axis ("the 'x' value").

ACCURACY:

The closeness of results of observations, computations or estimates to the true values or the values accepted as being true.

ALTITUDE:

Elevation above or below a reference datum, as defined in Federal Information Processing Standard 70-1. See also elevation.

ARC:

A locus of points that forms a curve that is defined by a mathematical expression.

AREA:

A generic term for a bounded, continuous, two-dimensional object that may or may not include its boundary.

ATTRIBUTE:

A defined characteristic of an entity type (e.g. composition).

ATTRIBUTE VALUE:

A specific quality or quantity assigned to an attribute (e.g. steel), for a specific entity instance.

CARTOGRAPHIC FEATURE FILE (CFF):

CFF's are base line data gathered from the Forest Service's Primary Base Series Quads. These maps are 7.5' quads mapped at a scale of 1:24,000 (Alaska differs from this standard) and contain the parent GIS layers including roads, streams, landnet, surface ownership and other misc. constructed features.

CLEARINGHOUSE:

See National Geospatial Data Clearinghouse.

COMPOUND ELEMENT:

A group of data elements and other compound elements. Compound elements represent higher-level concepts that cannot be represented by individual data elements.

COORDINATES:

Pairs of numbers expressing horizontal distances along orthogonal axes; alternatively, triplets of numbers measuring horizontal and vertical distances.

DATA ELEMENT:

A logically primitive item of data.

DATA SET:

A collection of related data. See also geospatial dataset.

DIGITAL IMAGE:

A two-dimensional array of regularly spaced picture elements (pixels) constituting a picture.

DOMAIN:

In the definition of the elements in the metadata standard, the domain identifies valid values for a data element.

E

ELEMENT:

Elements are the parts of the Sections or chapters within FGDC Content Standards for Digital Geospatial Metadata. They are numbered starting with the Section number. A set of elements with subparts is called a compound element, for example, 2.1.1 (Data Quality Information, Attribute Accuracy, Attribute Accuracy Report.)

There are 334 different elements in the FGDC standard, 119 of which exist only to contain other elements.

ELEVATION:

Conforming to Federal Information Processing Standard 70-1, the term "altitude" is used in this standard, rather than the common term elevation.

ENTITY INSTANCE:

A spatial phenomenon of a defined type that is embedded in one or more phenomena of different type, or that has at least one key attribute value different from the corresponding attribute values of surounding phenomena (e.g. 10 Steel Bridge).

EXECUTIVE ORDER 12906 :

Published in the April 13, 1994, edition of the Federal Register, Volume 59, Number 71, pp. 17671-17674

This Order calls for the establishment of the National Spatial Data Infrastructure defined as the technologies, policies, and people necessary to promote sharing of geospatial data throughout all levels of government, the private and non-profit sectors, and the academic community.

F

FGDC

The Federal Geographic Data Committee (FGDC) is an interagency committee, organized in 1990 under OMB Circular A-16 that promotes the coordinated use, sharing, and dissemination of geospatial data on a national basis. The FGDC is composed of representatives from seventeen Cabinet level and independent federal agencies.

FEATURE LEVEL DATA:

A feature is the spatial representation of the theme within a datase, for example, a particular stream, road, campground, vegetative community, or soil type.  You can see features on the computer screen ususually as points, lines, or polygons,

Metadata describing an individual feature is a part of the attribute file of the dataset rather than an FGDC metadata record. An example of  feature level metadata might show the source information used to input a particular road segment and a date when the segment was entered.

FGDC CLEARINGHOUSE:

The distributed discovery mechanism for digital geospatial data. Using the data elements defined in the Content Standards for Digital Geospatial Metadata, governmental, non-profit, and commercial participants worldwide can make their collections of spatial information searchable and accessible on the Internet using this free reference implementation software developed by the FGDC called the FGDC Clearinghhouse.

A clearinghouse is a decentralized system of servers located on the Internet which contain field-level descriptions of available digital spatial data. This descriptive information, known as metadata, are collected in a standard format to facilitate query and consistent presentation across multiple participating sites. Clearinghouse uses readily available Web technology for the client side and uses the ANSI standard Z39.50 for the query, search, and presentation of search results to the Web client.

FGDC CLEARINGHOUSE NODE:

Implementors of a clearinghouse must have access to multi-user computers (UNIX or Windows-NT) upon which the server software, interfaces, and metadata collections are stored. Server sites are connected to the Internet via dedicated, high-speed data connection of 56KB or greater. It is recommended that Clearinghouse servers be located coincident with spatial data collections to encourage synchronization between the spatial data and the metadata, or descriptions, being served. Organizations not yet connected to the Internet or who have firewall or security restrictions on being directly connected may elect to contract with an existing Internet Service Provider or partner with a local Clearinghouse node in a different organization to provide an off-site host computer for Clearinghouse.

FGDC COMPLIANT METADATA:

To be compliant with the FGDC metadata standard, a metadata record must successfully pass through the FGDC metaparser . The metaparser is often run directly from the metadata creation tool such as Metalite but can also be run separately.  If the record is incomplete or improperly formatted the metaparser will flag the errors.

In general terms, FGDC compliant metadata can be relatively simple or complex depending on the number of elements that are required.  If the metadata exists for a required element, it should be completed.

FGDC METADATA CONTENT STANDARDS

The standard was developed from the perspective of defining the information required by a prospective user to determine the availability of a set of geospatial data, to determine the fitness the set of geospatial data for an intended use, to determine the means of accessing the set of geospatial data, and to successfully transfer the set of geospatial data. As such, the standard establishes the names of data elements and compound elements to be used for these purposes, the definitions of these data elements and compound elements, and information about the values that are to be provided for the data elements. The standard does not specify the means by which this information is organized in a computer system or in a data transfer, nor the means by which this information is transmitted, communicated, or presented to the user.

FORMAL METADATA:

Metadata records that conform to FGDC Metadata Content Standards.  

GEOSPATIAL DATA:

Information that identifies the geographic location and characteristics of natural or constructed features and boundaries on the earth. This information may be derived from, among other things, remote sensing, mapping, and surveying technologies.

GEOSPATIAL DATASET:

Group of data that represent one or more themes and reside in one place such as a coverage and shapefile. It usually includes both spatial data and the tabular data that describe the spatial features.   

GRID:

(1) a set of grid cells forming a regular, or nearly regular, tessellation of a surface; (2) a set of points arrayed in a pattern that forms a regular, or nearly regular, tesselation of a surface. The tessellation is regular if formed by repeating the pattern of a regular polygon, such as a square, equilateral triangle, or regular hexagon. The tessellation is nearly regular if formed by repeating the pattern of an "almost" regular polygon such as a rectangle, non-square parallelogram, or non-equilateral triangle.

GRID CELL:

a two-dimensional object that represents the smallest nondivisible element of a grid.

HORIZONTAL:

Tangent to the geoid or parallel to a plane that is tangent to the geoid.

I

INTERIOR AREA:

An area not including its boundary.

LABEL POINT:

A reference point used for displaying map and chart text (e.g., feature names) to assist in feature identification.

LATITUDE:

Angular distance measured on a meridian north or south from the equator.

LAYER:

An integrated, areally distributed, set of spatial data usually representing entity instances within one theme, or having one common attribute or attribute value in an association of spatial objects. In the context of raster data, a layer is specifically a two-dimensional array of scaler values associated with all of part of a grid or image.

LEGACY DATA:

LINE:

A generic term for a one-dimensional object.

LINE SEGMENT:

A direct line between two points.

LONGITUDE:

Angular distance between the plane of a meridian east or west from the plane of the meridian of Greenwich.

M

MAP:

A spatial representation, usually graphic on a flat surface, of spatial phenomena.

MEDIA:

The physical devices used to record, store, and (or) transmit data.

MERIDIAN:

A great circle on the Earth that passes through the geographic poles.

METADATA:

Data about the content, quality, condition, and other characteristics of data. Data about data

METADATA CREATION TOOL:

Software used to create metadata records.

METADATA RECORD:

Metadata that describe spatial (map) data and related tabular data for a dataset. Metadata records use the standardized FGDC format so they can be searched on the World Wide Web.

METALITE:

A tool built for the purpose of creating FGDC compliant metadata. Refer to "Tools" in this User Guide for a description of this tool.

METAPARSER:

Designed to parse metadata encoded as indented text, check the syntactical structure against the standard, and reexpress the metadata in several useful formats (HTML, SGML, TEXT, and DIF).

MP is a tool to check syntactical structure, not accuracy

N

NATIONAL GEOSPATIAL DATA CLEARINGHOUSE:

A distributed network of geospatial data producers, managers, and users linked electronically. Building on initiatives such as the national information infrastructure, the clearinghouse uses a distributed, electronically connected network, such as the Internet. Each data provider will describe available data in an electronic form, and provide these descriptions (or "metadata") using means that can be accessed over a communications network. Thus, the data for the clearinghouse are located at the sites of data producers (or, where more efficient, at the sites of intermediaries) throughout the country. Using the network, users will search these descriptions to locate data that are suitable for their applications.

NOAA METADATA TOOL:

A tool built for the purpose of creating FGDC compliant metadata. Refer to "Tools" in this User Guide for a description of this tool.

NODE:

A zero-dimensional object that is a topological junction of two or more links or chains, or an end point of a link or chain.

NSDI:

National Spatial Data Infrastructure (NSDI)

The NSDI encompasses policies, standards, and procedures for organizations to cooperatively produce and share geographic data. The 17 federal agencies that make up the FGDC are developing the NSDI in cooperation with organizations from state, local and tribal governments, the academic community, and the private sector. FGDC coordinates development of NSDI.

ORDINATE:

The coordinate of a point in a plane cartesian coordinate system obtained by measuring parallel to the y-axis ("the 'y' value").

PIXEL:

Two-dimensional picture element that is the smallest nondivisible element of a digital image.

POINT:

A zero-dimensional object that specifies geometric location. One coordinate pair or triplet specifies the location. Area point, entity point, and label point are special implementations of the general case.

QUALITY:

An essential or distinguishing characteristic necessary for cartographic data to be fit for use.

RASTER:

One or more overlapping layers for the same grid or digital image.

RASTER OBJECT:

One or more images and/or grids, each grid or image representing a layer, such that corresponding grid cells and/or pixels between layers are congruent and registered.

REQUIRED OUTPUT FILES:

Files generated by the metaparser. These include:

• SGML - Used for Clearinghouse publication
• TXT - Used for clearinghouse publication
• HTML - Used for web publication including on a clearinghouse.
• XML- New web format more robust than HTML

RESOLUTION:

The minimum difference between two independently measured or computed values which can be distinguished by the measurement or analytical method being considered or used.

S

SECTIONS (of Metadata Content Standards)

Sections are the numbered categories or chapters of metadata elements within the FGDC Content Standards for Digital Geospatial Metadata. They are: 1. Identification, 2. Data Quality, 3. Spatial Data Organization, 4. Spatial Reference, 5. Entity and Attribute, 6. Distribution, 7. Metadata Reference.

SDTS:

The Spatial Data Transfer Standard defined by Department of Commerce, 1992, Spatial Data Transfer Standard (SDTS) (Federal Information Processing Standard 173): Washington, Department of Commerce, National Institute of Standards and Technology.

SPATIAL DATA:

Data that record the geographic location and shape of geographic features and their spatial relationships to other features" (ESRI).

T

TABULAR DATA:

Data describe things using characters and numbers formatted into columns and rows.  

THEME:

Group of data that represent a place or thing such as soils, vegetation, or roads. A theme could be less concrete such as population density, school districts, or administrative boundaries.

TYPE:

In the definition of the elements in the metadata standard, a compound element has the type "compound" to provide a unique way to identify compound elements. For a data element, the type identifies the kind of value that can be assigned to the data element. The choices are "integer" for integer numbers, "real" for real numbers, "text" for ASCII characters, "date" for day of the year, and "time" for time of the day.

UNIVERSAL POLYGON:

Defines the part of the universe that is outside the perimeter of the area covered by other GT-polygons ("covered area") and completes the two-dimensional manifold. This polygon completes the adjacency relationships of the perimeter links. The boundary of the universe polygon is represented by one or more inner rings and no outer ring. Attribution of the universe polygon may not exist, or may be substantially different from the attribution of the covered area.

VECTOR:

Composed of directed lines.