Gis_1

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Geographic Information Systems

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A computer system capable of capturing, storing, analyzing, and displaying geographically referenced (according to location) information.

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Vector Model

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A spatial data storage method in which features are represented by one or more pairs of x-y coordinate values forming points, lines, or polygons.

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Raster Model

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A data model that uses rasters or numeric arrays to represent real-world features.

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Geo-referenced

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A spatial data layer that is tied to a specific location on the earth's surface for display with other data.

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Features

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A spatial object composed of one or more x-y coordinate pairs and having on or more attributes in a single record of an associated table.

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Point

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A one-dimensional feature defined by a single x-y coordinate pair such as a well.

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Line

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A spatial feature composed of a string of x-y coordinate vertices and used to represent linear features such as streets.

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Polygons

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A closed two-dimensional area feature defined by three or more x-y coordinate pairs.

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Nodes

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The beginning and endpoint of a line feature.

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Vertex

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A point at which the segments of a line or polygon feature change direction.

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Feature Classes

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A set of similar objects with the same attributes stored together in a spatial data file.

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Attributes

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Information about map features stored in columns of a table.

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Feature ID

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(FID) A unique number assigned to every feature in a spatial data file and used for identification and tracking.

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Object ID

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(OID) Unique number identifying a row in a table or a feature in a geodatabase feature class.

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Thematic mapping

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Displaying the features of a spatial data layer based on values in its attribute table.

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Feature Datasets

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A set of feature classes in a geodatabase that share a common coordinate system and can participate in networks and topology.

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Spaghetti Models

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A model that stores spatial features as a series of x-y coordinates and does not store topological relationships between features.

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Topological Models

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A data model that stores spatial relationships between features in addition to their x-y coordinates.

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Adjacency

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A spatial condition that quantifies whether one feature touches another.

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Connectivity

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A property of linear features when they are connected to each other via junctions.

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Connectivity

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A property of linear features when they are connected to each other via junctions.

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Overlap

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A spatial condition that quantifies whether one feature covers all or part of another feature.

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Intersection

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The property of two features touching each other in whole or in part.

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Logical Consistency

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A measure of how well data features represent real-world features, in particular with respect to topology.

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Cells

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A square data element in a raster corresponding to one value representing conditions on the ground.

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Pixels

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A square data element in a raster corresponding to one value representing conditions on the ground.

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Discrete

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Data that take on a relatively small number of distinct values.

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Digital Elevation Model

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(DEM) A raster array of values representing elevations at the earth's surface.

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Continuous

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Data that take on a variety of different values and that change rapidly across a data set, such as elevation.

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Bands

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A single array of values stored in a raster, which may store one array or many.

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Digital Raster Graphic

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(DRG) A scanned image of a USGS topographic map.

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Resolution

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(1) The ground area represented by one cell value in a raster
(2) The default storage precision of a vector data set.

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Coordinate System

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(1) A specified range of x-y values onto which a map is plotted
(2) The definition of a coordinate space used by a map layer, including the ellipsoid, datum, and projection.

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Geographic Coordinate System

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(GCS) A spherical coordinate system of degrees of latitude and longitude that is used to locate features on the earth's surface.

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Map Units

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The units of the coordinate system in which a map is stored or displayed.

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Map Scale

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The ratio of feature size on a map to its size on the ground.

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Geometric Accuracy

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The accuracy with which the shape and position of features are represented.

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Thematic Accuracy

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The degree to which attribute values represent the true properties in the real world.

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Precision

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The number of digits allotted to store a numeric value.

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Metadata

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Information stored about data to document its source, history, management, uses, and more.

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dBase

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A database program whose file format has been adopted for the shapefile data model and tables in ArcGIS.

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Multipart Feature

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A single feature composed of non-touching units, such as a single state feature composed of the seven Hawaiian islands.

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Network Topology

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An association of linear edges and connecting points, used to model the flow of a commodity, such as traffic or utilities.

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Planar Topology

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An association of feature classes in a featue dataset, established by rules regarding the spatial relationships between features, such as not overlapping each other.

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Domains

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A rule that determines the values that may be entered into an attribute.

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Datum

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A combination of an earth ellipsoid and a reference point to reduce mapping discrepancies for a particular region.

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Coverage

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The spatial data format created for and used by, ArcInfo.

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Image Service

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An internet map layer that is available for viewing but that cannot be downloaded for local storage by the user.

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Feature Service

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An internet map layer in which the actual features may be downloaded by the user and saved locally.

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Folder Connections

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(1) A link in ArcCatalog and ArcMap that point to a folder with GIS data and serves as a shortcut to frequently used folders
(2) A link to a DBMS allowing data to be transferred.

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Thumbnail

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A small snapshot showing the appearance of a data layer and displaying in ArcCatalog to aid the user in finding data.

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Table of Contents

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The ArcMap window that lists the data frames and layers in the map document.

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Data Frame

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Container holding layers that are viewed and analyzed together; a map view.

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Layer

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A reference to a feature class and its associated properties.

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Layer File

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A file that stores a pointer to spatial data along with information on how to display it.

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Scale Range

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The range of scales for which a data layer will be displayed, set by the user to avoid clutter, or the display of layers at inappropriate scales.

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Digital Raster Graphic

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(DRG) A scanned image of a USGS topographic map.