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Glossary of GIS Terms

Why a glossary?

Terminology can be confusing in GIS; the following examples define terms used on the CUGIR site or found frequently in GIS-related materials.

Please suggest any other terms you would like a definition for, or how we could make our terminology more consistent or more clear.

Attribute Table

An attribute table is a database table containing information about geographic features in a GIS dataset. One column typically contains a primary geographic identifier (such as a census tract ID number). Other columns might contain additional geographic information (such as a county FIPS code or state abbreviation), spatial information such as line length or polygon area, and/or associated data values such as population.

Content Standard for Digital Geospatial Metadata (CSDGM)

The FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998) provides 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. All CUGIR metadata are created in accordance with the FGDC CSDGM standard.

See also the CUGIR Help section on GIS metadata standards.

Coordinate System

A system of measurement for calculating and describing positions on the earth. There are two types of coordinate systems, geographic and projected. Geographic coordinate systems use latitude and longitude coordinates to reference real world locations, and are based on a spherical model (spheroid) of the earth. Projected coordinate systems use mathematical formulas to convert latitude and longitude coordinates from a three-dimensional surface to a two-dimensional surface.

See also the CUGIR Help section on data projections.

Data Dictionary

A data dictionary is a collection of descriptions of the data objects or items in a dataset for the benefit of users who need to refer to them; information is stored on all the objects within the database and their relationships with each other. Certain metadata records include or reference data dictionaries, and data dictionaries are sometimes included with CUGIR datasets.

Data Format

CUGIR distributes data in a number of digital formats, principally Arc Export, Shapefile, DEM, and GeoTIFF. Many of these formats are binary and therefore readable only with GIS software. Please see the help section on File Formats and GIS Software Compatibility for a more detailed discussion of each format. Data formats currently included in CUGIR are described in the Data Formats help section.

Data Provider

A data provider is a department, institution, government agency, other organization or individual that has provided data directly or indirectly to CUGIR. CUGIR users may browse data by provider via the Browse page, or select from the list of current data providers.

Data Theme

A data theme is a collection of geographic data published for one or more geographic areas (mapsheets in CUGIR). Most geographic datasets have accompanying attribute data in an attribute table. For example, the data theme Agricultural Districts includes 53 data files, one for each of the counties for which digital agriculture district data are available. Themes are assigned to topic categories to facilitate browsing by topic. Themes are divided into current and older versions, when appropriate.

Datum

A frame of reference or surface against which position measurements are made, based on an associated model of the shape of the earth (spheroid). Datums define the origin and orientation of latitude and longitude lines, or the position of the spheroid relative to the center of the earth.

Digital Raster Graphic (DRG)

A digital raster graphic (DRG) is a scanned image of a U.S. Geological Survey (USGS) standard series topographic map. The DRGs in CUGIR are supplied by the New York State Department of Environmental Conservation, and have had the map collars (including legend) removed to facilitate their use in GIS software. They are distributed by 7.5 minute quads (1:24,000 scale).

Extensible Markup Language (XML)

XML is a simple, very flexible text format derived from SGML (ISO 8879). Originally designed to meet the challenges of large-scale electronic publishing, XML is also playing an increasingly important role in the exchange of a wide variety of data on the Web and elsewhere. CUGIR metadata are stored as XML files, to which stylesheets are applied for display in a web browser.

Federal Geographic Data Committee (FGDC)

The Federal Geographic Data Committee is an interagency committee composed of representatives from the Executive Office of the President, Cabinet-level and independent agencies. The FGDC is developing the National Spatial Data Infrastructure (NSDI) in cooperation with organizations from State, local and tribal governments, the academic community, and the private sector. The NSDI encompasses policies, standards, and procedures for organizations to cooperatively produce and share geographic data.

FIPS Code

The Federal Information Processing Standard (FIPS), contains codes for named populated places, primary county divisions, and other locational entities of the United States and areas under the jurisdiction of the United States. The USGS maintains a searchable database for FIPS codes.

Gazetteer

A gazetteer is a geographical database or directory of place names and natural, historical, or cultural features. The CUGIR gazetteer was produced by the USGS Geographic Names Information System (GNIS).

Geographic Feature

A geographic feature is place or natural, historical, or cultural landmark as identified in the USGS Geographic Names Information System (GNIS), the source gazetteer for CUGIR. Each feature in the CUGIR gazetteer is linked to the USGS 7.5 minute quadrangle and county in which it is located.

International Standards Organization (ISO)

The ISO is a network of the national standards institutes of more than 150 countries, with a Central Secretariat in Geneva, Switzerland, that coordinates the system. The ISO Geographic Information / Geomatics technical committee 211 (TC211) develops standards that specify, for geographic information, methods, tools and services for data management (including definition and description), acquiring, processing, analyzing, accessing, presenting and transferring such data in digital / electronic form between different users, systems and locations. The TC211's published standard for Geographic information -- metadata (ISO 19115:2003) defines the schema required for describing geographic information and services. It provides information about the identification, the extent, the quality, the spatial and temporal schema, spatial reference, and distribution of digital geographic data.

Large Scale Hydrography

The New York State Large Scale Hydrography dataset contains information about surface and network water features such as lakes, ponds, streams, rivers, springs and wells. The NYS Large Scale Hydrography dataset is similar to National Hydrography Dataset (NHD) data in that it is tiled by subbasin and is networked (has center lines and connectors to represent continuous linear flow). NHD also includes a flow table, reach codes, and many other features the NYS Hydrography Network does not yet have.

Mapsheet

A mapsheet is a geographic unit or identifiable spatial area for which one or more data themes are available. Mapsheets are grouped into spatial series, examples of which include the 62 New York counties, more than 900 7.5 minute quadrangles, 18 1x2-degree quadrangles, the Hudson River Estuary, and New York State as a whole.

National Hydrography Dataset (NHD)

The National Hydrography Dataset (NHD) is a comprehensive set of digital spatial data that contains information about surface water features such as lakes, ponds, streams, rivers, springs and wells.

See also the CUGIR Help section on Large Scale Hydrography.

National Spatial Data Infrastructure (NSDI)

The National Spatial Data Infrastructure (NSDI) consists of the technology, policies, criteria, standards and people necessary to promote geospatial data sharing throughout all levels of government, the private and non-profit sectors, and academia. The Federal Geographic Data Committee (FGDC) coordinates the development of the NSDI. CUGIR is an active online repository of the NSDI program.

Projection

A mathematically based process for converting locations on the three-dimensional earth surface into two dimensions. Spherical coordinates are converted to planar. Different projections will have differing impacts on various aspects of area, distance, and shape.

See also the CUGIR Help section on Data projections.

Spatial Series

A spatial series is a collection of mapsheets (discrete spatial units) for which one or more data themes are available in CUGIR. For example, the spatial series New York counties includes 62 mapsheets (one for each county), and there are more than 40 data themes available for this spatial series. CUGIR users may browse data by spatial series via the Browse page, or select from a list of current spatial series.

Spheroid

A mathematically derived model depicting the size and shape of the earth.

Topic

One or more topics are assigned to each data theme. CUGIR users may browse data by topic via the Browse page, or select from current ISO topics represented within CUGIR's collection.

Version

Since CUGIR's inception in 1998, many of the data themes in CUGIR have been updated or replaced by more recent data. Because newer versions may involve significant changes in scope, definition, scale, or other factors, CUGIR sometimes treats each version as a separate data theme, and current and older data files are sometimes separated for display in CUGIR. The decision to make older versions of data publicly available or not rests with the data provider.