GIS Glossary/O

GIS Glossary

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object
In GIS, a digital representation of a spatial or nonspatial entity. Objects usually belong to a class of objects with common attribute values and behaviors.

object class
In a geodatabase, a collection of nonspatial data of the same type or class. While spatial objects (features) are stored in feature classes in a geodatabase, nonspatial objects are stored in object classes.

Object Definition Language
Similar to Interface Definition Language, but used to define the objects contained in an object library.

object library
A binary file that stores information about a logical collection of COM objects and their properties and methods in a form that is accessible to other applications at run time. Using a type library, an application or browser can determine which interfaces an object supports and invoke an object's interface methods.

object model diagram
A graphical representation of the types in a library and their relationships.

object pooling
The process of precreating a collection of instances of classes, such that the instances can be shared between multiple application sessions at the request level. Pooling objects allows the separation of potentially costly initialization and acquisition of resources from the actual work the object does. Pooled objects are used in a stateless manner.

object view
A philosophical view of geographic space in which space is seen as empty except where occupied by objects. In this view, every spatial location is either something (an object) or nothing.

ObjectID
In ArcGIS, a system-managed value that uniquely identifies a record or feature.

object-oriented database
A data management structure that stores data as objects (instances of a class) instead of as rows and tables as in a relational database.

object-oriented programming
A programming model in which related tasks, properties, and data structures are enclosed inside an object, and work is done when objects make requests and receive results from other objects. For example, a billing program may contain an object that maintains customer records. That object may pass information to another object that handles mailing statements, and another object that handles customer payments may ask it to update a customer record when a payment is received.

oblate ellipsoid
An ellipsoid created by rotating an ellipse around its minor axis. The shape of the earth approximates an oblate ellipsoid with a flattening ratio of 1 to 298.257.

oblate spheroid
An ellipsoid created by rotating an ellipse around its minor axis. The shape of the earth approximates an oblate ellipsoid with a flattening ratio of 1 to 298.257.

oblique aspect
A planar or cylindrical projection whose point of tangency is neither on the equator nor at a pole.

oblique photograph
An aerial photograph taken with the axis of the camera held at an angle between the horizontal plane of the ground and the vertical plane perpendicular to the ground. A low oblique image shows only the surface of the earth; a high oblique image includes the horizon.

oblique projection
A planar or cylindrical projection whose point of tangency is neither on the equator nor at a pole.

observer
In ArcScene and ArcGlobe, the position of the camera in a scene or globe.

observer offset
In ArcScene and ArcGlobe, the height of the observer point above a surface used in analysis when calculating lines of sight and viewsheds.

OCS
Acronym for output coordinate system. In ArcWeb Services, a user-defined map projection.

OCX
Also known as an ActiveX control, an OLE custom control is contained in a file with the extension .ocx. The ArcGIS controls are ActiveX controls.

OD cost matrix
In ArcGIS Network Analyst, a type of network analysis that computes a table containing the total impedance from each origin to each destination. Additionally, it ranks the destinations that each origin connects to in ascending order of the time it takes to travel from that origin to each destination.

ODL
Acronym for Object Definition Language. Similar to Interface Definition Language, but used to define the objects contained in an object library.

off-nadir
Any point not directly beneath a scanner's detectors, but rather off at an angle.

offset
In cartography, the displacement or movement of features so that they do not overlap when displayed at a given scale. For example, a road can be offset from a river if the symbols are wide enough that they overlap.

offset distance
The distance a label should be from the feature it labels. A label offset and a maximum label offset can be set for point features. Maximum label offsets are expressed as a percentage of the label offset. For line features, a label offset can be set from the line (similar to the label offset for point features) and along the line (which controls the position of the label relative to the ends of the line). Label offsets are not available for all label position options.

OGC
Acronym for Open Geospatial Consortium. An international consortium of companies, government agencies, and universities participating in a consensus process to develop publicly available geospatial and location-based services. Interfaces and protocols defined by OpenGIS specifications support interoperability and seek to integrate geospatial technologies with wireless and location-based services.

OGIS
Acronym for Open Geodata Interoperability Specification. A specification, developed by the Open Geospatial Consortium, Inc., to support interoperability of GIS in a heterogeneous computing environment.

OID
In ArcGIS, a system-managed value that uniquely identifies a record or feature.

OLB
Acronym for object library. A binary file that stores information about a logical collection of COM objects and their properties and methods in a form that is accessible to other applications at run time. Using a type library, an application or browser can determine which interfaces an object supports and invoke an object's interface methods.

OLE
Acronym for Object Linking and Embedding. A protocol from Microsoft that allows the development of reusable objects that can be exchanged by multiple applications. Applications using OLE can create compound documents that link to data in other applications. The data can be edited from the document without switching between applications.

OLE custom control
Also known as an ActiveX control, an OLE custom control is contained in a file with the extension .ocx. The ArcGIS controls are ActiveX controls.

OLE DB provider
Object Linking and Embedding database provider. A tool conforming to the OLE standard for sharing data between applications. Each OLE DB provider communicates with and retrieves data from a different database, but a user can work with the data retrieved by any OLE DB provider in a similar way.

OLE View
A utility, available as part of Microsoft Visual Studio, that can be used to view type information stored in a type library or object library or inside a DLL.

on the fly
Assembled, created, presented, or calculated dynamically during a transaction such as a Web page search or data display query.

on-demand cache
In ArcGlobe, a temporary layer cache that is placed on disk and built as areas of the layer are viewed.

one-to-many relationship
An association between two linked or joined tables in which one record in the first table corresponds to many records in the second table.

one-to-one relationship
An association between two linked or joined tables in which one record in the first table corresponds to only one record in the second table.

one-way replication
A type of geodatabase replication that allows data changes to be sent multiple times from the parent replica to the child replica. In a one-way replication, the data in the parent replica is editable, and the data in the child replica is read-only. During synchronization, edits are applied directly to the child replica so that no conflicts occur. ArcSDE geodatabases are used to create one-way replicas.

on-screen digitizing
Manual digitization by tracing a mouse over features displayed on a computer monitor, used as a method of vectorizing raster data.

ontology
In computer science, a data model that represents a domain by detailing the entities that comprise it and the semantic relationships between them. Ontologies generally include individuals, classes, attributes and relations.

Open Geodata Interoperability Specification
A specification, developed by the Open Geospatial Consortium, Inc., to support interoperability of GIS in a heterogeneous computing environment.

Open Geospatial Consortium
An international consortium of companies, government agencies, and universities participating in a consensus process to develop publicly available geospatial and location-based services. Interfaces and protocols defined by OpenGIS specifications support interoperability and seek to integrate geospatial technologies with wireless and location-based services.

open traverse
In surveying, a traverse that does not close back upon itself or on another point of known position. As such, it does not provide a means of checking for errors.

OpenGIS Consortium
Acronym for Open Geospatial Consortium. An international consortium of companies, government agencies, and universities participating in a consensus process to develop publicly available geospatial and location-based services. Interfaces and protocols defined by OpenGIS specifications support interoperability and seek to integrate geospatial technologies with wireless and location-based services.

OpenLS
Acronym for OpenGIS Location Services</I>. A protocol, designed to work across the many different wireless networks and devices, that allows seamless access to multiple content repositories and service frameworks.

operand
A data value or the symbolic representation of a data value in an expression. Operands may be numbers, character strings, functions, variables, parenthetical expressions in the body of a larger expression, and so on. Symbolic representations of operands, such as variables and functions, are evaluated before they are operated upon by the operators in the expression. For example, in the expression "1 + 2", the operands are 1 and 2, and are operated upon by the + (plus) operator, which adds the operands together and returns the value 3.

operation codes
In surveying, an alphanumeric or numeric value included in an instrument vendor's data collector file format. Operation codes are used to describe such elements as new instrument setups and numeric values for horizontal angles, zenith angles, slope distance measurements, height of instrument, and height of target. These basic operation codes are supported in Survey Analyst for field measurements for the following formats: Geoserial Interface (GSI), TDS raw, TDS coordinate, Geodimeter, and Sokkia SDR.

operator
The symbolic representation of a process or operation performed against one or more operands in an expression, such as "+" (plus, or addition) and "&gt;" (greater than). When evaluated, operators return a value as their result. If multiple operators appear in an expression, they are evaluated in order of their operator precedence.

operator precedence
The order in which operators are evaluated in an expression; operators with a higher precedence are evaluated before those with a lower precedence. If all operators in an expression have the same precedence, they are evaluated in the order in which they appear, from left to right. Parentheses may be used to override operator precedence; portions of an expression within parenthesis are evaluated first, and parenthetical expressions may be nested.

optical center
The point on a rectangular map or image to which the eye is drawn. The visual center lies slightly (about 5 percent of the total height) above the geometric center of the page.

optimization
The process of fine-tuning data, software, or processes to increase efficiency, improve performance, and produce the best possible results.

Oracle
A database company that produces a relational database management system (also called Oracle), which allows data and other objects to be stored in tables. Oracle provides client/server access to data and uses indexes, sequences, and other database objects to facilitate rapid data creation, editing, and access. ESRI uses Oracle's RDBMS to store vector and raster data for use by ArcSDE.

order
In ArcGIS Network Analyst, a network location used to determine routes in vehicle routing problem (VRP) analysis. Users can specify multiple orders. Orders may represent any combination of service locations or pickup/delivery locations to be visited along a route.

order pair
In ArcGIS Network Analyst, an object used in vehicle routing problem (VRP) analysis. An order pair defines a relationship between two orders. The first order in the order pair represents a pickup which must then be delivered to the second order in the order pair on the same route.

ordinal data
Data classified by comparative value; for example, a group of polygons colored lighter to darker to represent less to more densely populated areas.

ordinary kriging
A kriging method in which the weights of the values sum to unity. It uses an average of a subset of neighboring points to produce a particular interpolation point.

ordinate
In a rectangular coordinate system, the distance of the y-coordinate along a vertical axis from the horizontal or x-axis. For example, a point with the coordinates (7,3) has an ordinate of 3.

Ordnance Survey
The national mapping and cartographic agency of the United Kingdom. Now a civilian organization, the Ordnance Survey is one of the world's largest producers of maps and was the first national mapping organization in the world to complete a large-scale program of digital mapping.

orientation
An object's position or relationship in direction with reference to points of the compass.

orientation of vertical labels
An option that controls whether a label can be placed in an upside-down or sideways position. A small angle prevents labels from switching their reading order in the labeling of nearly vertical lines.

origin
A fixed reference point in a coordinate system from which all other points are calculated, usually represented by the coordinates (0,0) in a planar coordinate system and (0,0,0) in a three-dimensional system. The center of a projection is not always its origin.

origin-destination cost matrix
In ArcGIS Network Analyst, a type of network analysis that computes a table containing the total impedance from each origin to each destination. Additionally, it ranks the destinations that each origin connects to in ascending order of the time it takes to travel from that origin to each destination.

orthocorrection
The process of correcting the geometry of an image so that it appears as though each pixel were acquired from directly overhead. Orthorectification uses elevation data to correct terrain distortion in aerial or satellite imagery.

orthogonal
Intersecting at right angles.

orthogonal offset
A line that is perpendicular to another line at its point of tangency, often used to measure distance from a line to a separate point that does not lie along the original line.

orthographic projection
A planar projection, tangent to the earth at one point, that views the earth's surface from a point approaching infinity, as if from deep space.

orthographic view
In 3D Analyst, a perspective that allows viewing of data in a scene as a two-dimensional plane seen from above. There is no perspective foreshortening in orthographic view, so scale is constant across the entire display.

orthomorphic projection
A projection that preserves the correct shapes of small areas. In a conformal projection, graticule lines intersect at 90-degree angles, and at any point on the map the scale is the same in all directions. A conformal projection maintains all angles at each point, including those between the intersections of arcs; therefore, the size of areas enclosed by many arcs may be greatly distorted. No map projection can preserve the shapes of larger regions.

orthophotograph
An aerial photograph from which distortions owing to camera tilt and ground relief have been removed. An orthophotograph has the same scale throughout and can be used as a map.

orthophotoquad
An orthophotograph that has been formatted as a USGS 1:24,000 topographic quadrangle with little or no cartographic enhancement.

orthophotoscope
A photomechanical or optical-electronic device that creates an orthophotograph by removing geometric and relief distortion from an aerial photograph.

orthorectification
The process of correcting the geometry of an image so that it appears as though each pixel were acquired from directly overhead. Orthorectification uses elevation data to correct terrain distortion in aerial or satellite imagery.

outbound interface
An interface implemented by a class, on which that object can make calls to its clients; analogous to a callback mechanism.

outlier
An unusual or extreme data value in a dataset. In data analysis, outliers can potentially have a strong effect on results and so must be analyzed carefully to determine if they represent valid or erroneous data.

outline
The path that follows the boundary of an object. Outlines are also called strokes.

outline vectorization
A vectorization method that generates lines along the borders of connected cells. It is typically used for vectorizing scanned land-use and vegetation maps.

out-of-process
Within the process space of a client application, a component contained in an EXE is out-of-process; instantiated classes are loaded into the process space of the EXE in which they are defined rather than into that of the client.

output coordinate system
In ArcWeb Services, a user-defined map projection.

output data
Data that is the result of a computer, device, program, or process.

output directory
In ArcIMS, the folder designated during installation to hold files being served to users for display in a browser.

overflow list
A list of labels that could not be placed, generated during the process of converting labels to annotation. This list allows the manual placement or deletion of these labels.

overlapping rings
A method of defining the rings in an analysis so that the values inside the rings are cumulative. For example, if you had an analysis with three concentric rings and 10 households in each, the total number of households for ring 1 would be 10, the total for ring 2 would be 20 (ring 1 + ring 2), and the total for ring 3 would be 30 (ring 1 + ring 2 + ring 3).

overlay
A spatial operation in which two or more maps or layers registered to a common coordinate system are superimposed, either digitally or on a transparent material, for the purpose of showing the relationships between features that occupy the same geographic space.

overlay events
In linear referencing, an operation that produces a route event table that is the logical intersection or union of two input route event tables. Event overlay is one way to perform line-on-line, line-on-point, and event point-on-point overlays.

Overlay Wizard
In ArcGIS 8.3 and previous versions, an ArcToolbox wizard that uses overlay operations to create a new coverage by computing the geometric intersection of two coverages: an input coverage and an overlay coverage.

overprinting
In cartography, portraying cartographic updates on a map by printing new or modified information over the original cartography, usually in a distinctive color.

override
In network datasets, a type of junction connectivity policy in which the way junctions connect to other junctions is not based on the existing edge connectivity policy; junctions "override" the edge connectivity policy.

overshoot
The portion of an arc digitized past its intersection with another arc.

overview map
A generalized, smaller-scale map that shows the limits of another map's extent along with its surrounding area.

overview terrain
Coarsest representation of the terrain dataset, intended for fast drawing at small scales.

overview window
A secondary window in ArcMap data view that shows the full extent of the data, without changing the map extent. A red box in the window represents the current map extent.

owner
In ArcWeb Services, the person responsible for creating and maintaining a layer or service. The owner determines who has access to the content and the content permissions.