GIS Glossary/U

GIS Glossary

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USGS|U.S.G.S.
Acronym for United States Geological Survey. A scientific agency of the United States government, part of the Department of the Interior. The U.S. Geological Survey is a fact-finding research agency that monitors, analyzes, and provides scientific understanding about natural resource issues and conditions, the environment, and natural hazards. The U.S. Geological Survey is the primary civilian mapping agency in the United States. It produces digital and paper map products; aerial photography; and remotely sensed data on land cover, hydrology, geology, biology, and geography.

U.S. National Geodetic Survey
The U.S. government agency responsible for maintaining the National Spatial Reference System (NSRS), the national coordinate system of the United States.

UDDI
Acronym for Universal Description, Discovery, and Integration. An XML-based standard for creating online directories of Web services.

UI
Acronym for user interface. The portion of a computer's hardware and software that facilitates human interaction. The UI includes items that can be displayed on screen, and interacted with by using the keyboard, mouse, video, printer, and data capture.

UIControl
A custom button, tool, text box, or combo box created with VBA.

UML
Acronym for Unified Modeling Language. A modeling language that uses a series of diagrams to model the objects in a system.

unbuild parcel
In Survey Analyst - Cadastral Editor, a cadastral fabric editing command that undoes the parcel generated from the build parcel command.

UNC
Acronym for Universal (or Uniform) Naming Convention. A PC format for specifying the location of resources on a local-area network (LAN). UNC follows the format \\servername\shared_resource_path

uncertainty
The degree to which the measured value of some quantity is estimated to vary from the true value. Uncertainty can arise from a variety of sources, including limitations on the precision or accuracy of a measuring instrument or system; measurement error; the integration of data that uses different scales or that describe phenomena differently; conflicting representations of the same phenomena; the variable, unquantifiable, or indefinite nature of the phenomena being measured; or the limits of human knowledge. Uncertainty is often used to describe the degree of accuracy of a measurement.

unclosed parcel
A parcel that is only partially defined or that is missing a sequence of one or more lines that would otherwise close the parcel back onto its point of beginning.

uncommitted read
The isolation level in an RDBMS specifying the minimum isolation from concurrent transactions. The transaction can read data that has been changed by concurrent transactions even before the changes are committed to the database.

undershoot
A line that falls short of another line that it should intersect.

undevelopable surface
A surface, such as the earth's, that cannot be flattened into a map without stretching, tearing, or squeezing it. To produce a flat map of the round earth, its three-dimensional surface must be projected onto a developable shape such as a plane, cone, or cylinder.

undirected network flow
A network state in which each edge may or may not have an associated direction of flow. In an undirected network flow, the resource that traverses a network's components can decide which direction to take, such as traffic in transportation systems.

uniform list
In Survey Analyst for field measurements, one of two types of lists in the List page. The uniform list has rows that represent survey objects of the same type.

uninitialized flow direction
A condition that occurs in a network when an edge feature is not connected through the network to sources and sinks or if the edge feature is only connected to sources and sinks through disabled features.

union
A topological overlay of two or more polygon spatial datasets that preserves the features that fall within the spatial extent of either input dataset; that is, all features from both datasets are retained and extracted into a new polygon dataset.

unique constraint
A DBMS-defined restriction specifying that each value stored in a column must be unique and that no other row can contain the same value.

unit of measure
A standard quantity used for measurements such as length, area, and height.

United States Geological Survey
A scientific agency of the U.S. government, part of the Department of the Interior. The U.S. Geological Survey is a fact-finding research agency that monitors, analyzes, and provides scientific understanding about natural resource issues and conditions, the environment, and natural hazards. The U.S. Geological Survey is the primary civilian mapping agency in the United States. It produces digital and paper map products; aerial photography; and remotely sensed data on land cover, hydrology, geology, biology, and geography.

univariate analysis
Any statistical method for evaluating a single variable, rather than the relationship between two or more variables.

univariate distribution
A function for a single variable that gives the probabilities that the variable will take a given value.

Universal Description, Discovery, and Integration
An XML-based standard for creating online directories of Web services.

universal kriging
A kriging method often used on data with a significant spatial trend, such as a sloping surface. In universal kriging, the expected values of the sampled points are modeled as a polynomial trend. Kriging is carried out on the difference between this trend and the values of the sampled points.

universal polar stereographic
A projected coordinate system that covers all regions not included in the UTM coordinate system; that is, regions above 84 degrees north and below 80 degrees south. Its central point is either the north or south pole.

Universal Soil Loss Equation
An erosion model developed by the Agricultural Research Service of the United States Department of Agriculture that computes average annual soil loss caused by rainfall and associated overland flow. Factors used in the equation include rainfall, soil characteristics, topography, and land use and land cover. Each major factor is divided into numerous subfactors.

universal time
A timekeeping system that defines local time throughout the world by relating it to time at the prime meridian. Universal time is based on the average speed at which the earth rotates on its axis. For official purposes, universal time has been replaced by coordinated universal time; universal time is, however, still used in navigation and astronomy. Different versions of universal time correct for irregularities in the earth's rotation and orbit.

Universal Transverse Mercator
A projected coordinate system that divides the world into 60 north and south zones, 6 degrees wide.

universe polygon
In coverages, the first record in a polygon attribute table, representing the area beyond the outer boundary of the coverage.

UNIX time
The number of seconds, in coordinated universal time format, since January 1, 1970 (the start of the UNIX system).

unjoined parcel
In Survey Analyst - Cadastral Editor, a parcel that has not been connected to the cadastral fabric, and that has its own local coordinate system.

unknown points
In Survey Analyst for field measurements, previously uncoordinated points.

unmanaged raster catalog
A raster catalog in which the raster datasets are not copied or altered by the geodatabase and there will only be a pointer connecting the raster catalog row to the raster datasets. Deleting a row in an unmanaged raster catalog will not delete the raster dataset from its storage location.

unprojected coordinates
A measurement of a location on the earth's surface expressed in degrees of latitude and longitude.

update-gram
In ArcGIS, the programming object that holds updates in a delta file.

UPS
Acronym for Universal Polar Stereographic. A projected coordinate system that covers all regions not included in the UTM coordinate system; that is, regions above 84 degrees north and below 80 degrees south. Its central point is either the north or south pole.

upstream
In network tracing, the direction along a line or edge that opposes the direction of flow.

urban geography
The field of geography concerning the spatial and cultural patterns and processes of cities and neighborhoods.

Urban Vector Map
A vector-based data product in vector product format (VPF), typically at larger scales ranging from 1:2,000 to 1:25,000. UVMap data is typically collected over densely populated urban areas.

URL
Acronym for uniform resource locator. A standard format for the addresses of Web sites. A URL may look like this: http://www.esri.com. The first part of the address indicates what protocol to use (such as http: or ftp:), while the second part specifies the IP address or the host name (including the domain name) where the Web site is located. An optional third part may specify the path to a specific file or resource (http://www.esri.com/products.html).

usage
The way in which statements in a command or programming language are actually used. In geoprocessing, usage for a tool or environment setting can be viewed at the command line.

usage time
The amount of time between when a client gets a reference to a service and when they release it.

User Account Administration
A Web site for accessing information about an ArcWeb account. This site allows users to activate an ArcWeb Services account, view usage of ArcWeb services, manage POI and address records, and manage groups and alerts.

user interface
The aspects of a computer system or program with which a software user can interact, and the commands and mechanisms used to control its operation and input data.

user name
The identification used for authentication when a user logs in to a program.

USGS
Acronym for United States Geological Survey. A scientific agency of the U.S. government, part of the Department of the Interior. The U.S. Geological Survey is a fact-finding research agency that monitors, analyzes, and provides scientific understanding about natural resource issues and conditions, the environment, and natural hazards. The U.S. Geological Survey is the primary civilian mapping agency in the United States. It produces digital and paper map products; aerial photography; and remotely sensed data on land cover, hydrology, geology, biology, and geography.

USLE
An erosion model developed by the Agricultural Research Service of the United States Department of Agriculture that computes average annual soil loss caused by rainfall and associated overland flow. Factors used in the equation include rainfall, soil characteristics, topography, and land use and land cover. Each major factor is divided into numerous subfactors.

UT
A timekeeping system that defines local time throughout the world by relating it to time at the prime meridian. Universal time is based on the average speed at which the earth rotates on its axis. For official purposes, universal time has been replaced by coordinated universal time; universal time is, however, still used in navigation and astronomy. Different versions of universal time correct for irregularities in the earth's rotation and orbit.

UTC
The official timekeeping system of the world's nations since 1972. It refers local time throughout the world to time at the prime meridian, and is based on atomic clocks, but is periodically artificially adjusted so as to always remain within 0.9 seconds of universal time. The adjustment is made by the addition of leap seconds to the course of atomic time. Coordinated universal time is abbreviated "UTC." (The abbreviation UTC does not represent the word order of "coordinated universal time" in either English or French. It is an extension of the "UT*" pattern established for versions of universal time.)

utility COM object
In ArcObjects, a COM object that encapsulates a large number of fine-grained ArcObjects method calls and exposes a single coarse-grained method call. Utility COM objects are installed on a GIS server and called by server applications to minimize the round-trips between the client application and the GIS server.

Utility Web Service
A SOAP Web service for changing the coordinate system and datum transformation of a geometry or envelope.

UTM
Acronym for Universal Transverse Mercator</I>. A projected coordinate system that divides the world into 60 north and south zones, 6 degrees wide.

UVMap
Acronym for Urban Vector Map</I>. A vector-based data product in vector product format (VPF), typically at larger scales ranging from 1:2,000 to 1:25,000. UVMap data is typically collected over densely populated urban areas.