- tablet
-
A small digitizer used for
interactive work on a graphics workstation. Tape drive A device for
reading and writing computer files on magnetic tape.
-
A set of data elements that
has a horizontal dimension (rows) and a vertical dimension (columns) in a
relational database system. A table has a specified number of columns but
can have any number of rows. A table is often called a relation. Rows
stored in a table are structurally equivalent to records from flat files
in that they must not contain repeating fields.
-
Text attribute table for an
annotation subclass in a coverage. In addition to user-defined attributes,
the TAT contains a sequence number and text feature identifier. See also
feature attribute table.
- TCP/IP
-
The Transmission Control
Protocol (TCP) is a communication protocol layered above the Protocol
(IP). These are low-level communication protocols which allow computers to
send and receive data.
- temporal resolution
-
Is a measure of how
frequently the remote sensing sensor will pass over the exact same
location. This is also called a revisit time. The lower this value becomes
the more often an image of the same spot can be acquired by the same
device..
- template
-
1. A coverage containing
common feature boundaries, such as land-water boundaries, for use as a
starting place in automating other coverages. Templates save time and
increase the precision of topological overlays.
2. A map template
containing neatlines, North arrow, logos, and other cartographic map
elements for a common map series.
3. An empty tabular data
file containing only item definitions.
- Terabyte, TB
-
A measure of data size. A
terabyte of data is equivalent to 1,000 gigabytes of data or 1,000,000
megabytes of data. One petabyte equals 1,000 terabytes. Computer unit, 1012
bytes.
- terminal
-
A device, usually a display
monitor and a keyboard, used to communicate with the computer.
- terrain analysis
-
Analytical techniques that
quantify terrain parameters (slope, aspect) or the effect of terrain on a
particular operation.
- tessellation
-
The process of splitting an
area into small, manageable units or sub-areas. Sub-areas may consist of
tiles or rasters.
-
A text style defined by
font, size, character spacing, color, and so on, used to label maps and
coverage features in ArcInfo.
- Thiessen polygons
-
Polygons whose boundaries
define the area that is closest to each point relative to all other
points. Thiessen polygons are generated from a set of points. They are
mathematically defined by the perpendicular bisectors of the lines between
all points. A tin structure is used to create Thiessen polygons.
- theme
-
A user-defined perspective
on a coverage, grid, tin or image geographic data set specified, if
applicable, by a coverage name and feature class or data set name,
attributes of interest, a data classification scheme, and theme-specific
symbology for drawing.
- thematic data
-
See
descriptive data.
- thiessen polygons
-
The process of splitting up
a study area such that all points in the sample area are grouped into
tiles according to the minimum distance between them and a previously
sampled point. Also known as Thiessen or Voronoi polygons.
- thinning
-
A process whereby a line is
generalized through a series of rules that reduce the number of data
points while maintaining the basic shape of the feature.
-
Registration or geographic
control points for a coverage representing known locations on the Earth's
surface. Tics allow all coverage features to be recorded in a common
coordinate system (e.g., Universal Transverse Mercator [UTM] meters or
State Plane feet). Tics are used to register map sheets when they are
mounted on a digitizer and to transform the coordinates of a coverage
(e.g., from digitizer units [inches] to UTM meters).
- TIC file
-
The coverage file used to
store tic coordinates and tic IDs for a coverage.
- tic match tolerance
-
The maximum distance
allowed between an existing tic and a tic being digitized. If this
distance is exceeded, the digitizing error is considered unacceptable and
the map must be registered over again. The tic match tolerance is used to
ensure a low
RMS
error during map registration on a digitizer.
-
Tagged interchange (image)
file format. An industry-standard raster data format. TIFF supports
black-and-white, gray-scale, pseudocolor, and true-color images, all of
which can be stored in a compressed or uncompressed format. TIFF is
commonly used in desktop publishing and serves as an interface to numerous
scanners and graphic arts packages. (See
CCITT.)
- TIGER
-
The Topologically
Integrated Geographic Encoding and Referencing data format used by the
U.S. Census Bureau to support census programs and surveys. It was used for
the 1990 census. TIGER files contain street address ranges along lines and
census tract/block boundaries. This descriptive data can be used to
associate address information and census/demographic data with coverage
features.
-
The spatial unit by which
geographic data is organized, subdivided, and stored in a map library.
Tiles subdivide the area covered by a map library and organize the library
data by location (e.g., counties might be the tiles in a statewide
database). A tile can be a regular, geometric shape (e.g., a map sheet),
or an irregular shape, such as a county boundary. See also
LIBRARIAN.
-
Triangulated irregular
network. A
surface representation derived from irregularly spaced sample points
and
breakline features. The tin data set includes topological
relationships between points and their neighboring triangles. Each sample
point has an x,y coordinate and a surface, or z-value. These points are
connected by edges to form a set of non-overlapping triangles used to
represent the surface. Tins are also called irregular triangular mesh or
irregular triangular surface model.
- TIN
-
The ArcInfo software
product used for
surface representation, modeling, and display.
- TOL file
-
A coverage file that
contains processing tolerances (fuzzy, tic match, dangle length) and
editing tolerances (weed, grain, edit distance, snap distance, and
nodesnap distance). ArcInfo uses TOL file values as defaults in many
automation, editing, and processing operations.
- to-node
-
Of an arc's two endpoints,
the one last digitized. See also
from-node.
-
1. A map containing
contours indicating lines of equal surface elevation (relief), often
referred to as topo maps.
2. Often used to refer to a
map sheet published by the U.S. Geological Survey in the 7.5-minute
quadrangle series or the 15-minute quadrangle series.
-
An analysis procedure for
determining the spatial coincidence of geographic features. ArcInfo
supports overlay among and between all
feature classes. See also
identity,
intersect and union.
-
The spatial relationships
between connecting or adjacent coverage features (e.g., arcs, nodes,
polygons, and points). For example, the topology of an arc includes its
from- and to-nodes, and its left and right polygons. Topological
relationships are built from simple elements into complex elements: points
(simplest elements), arcs (sets of connected points), areas (sets of
connected arcs), and routes (sets of sections, which are arcs or portions
of arcs). Redundant data (coordinates) are eliminated because an arc may
represent a linear feature, part of the boundary of an area feature, or
both. Topology is useful in GIS because many spatial modeling operations
don't require coordinates, only topological information. For example, to
find an optimal path between two points requires a list of the arcs that
connect to each other and the cost to traverse each arc in each direction.
Coordinates are only needed for drawing the path after it is calculated.
-
A tour is a minimum-impedance
path that starts at an origin, visits a number of stops and returns to the
origin visiting the stops only once. This is the solution to the traveling
salesman problem. ArcInfo provides a heuristic solution to the traveling
salesman problem by ordering the stops and then finding the
least-cost path which visits them.
- tracing
-
The process of determining
which portions of a network connect.
- trade-area map
-
A map showing the region
from which a store derives a certain percentage of its revenues.
Trade-area maps can be made from the information contained in an
interaction matrix.
-
A logical unit of work
performed on a database. A transaction can be terminated by either making
permanent or
rolling back all updates.
- transformation
-
The process that converts
coordinates from one coordinate system to another through translation,
rotation, and scaling. ArcInfo supports these transformations: similarity,
affine, piecewise linear, projective, NADCON datum adjustment using
minimum-derived curvature transformation, and a polynomial transformation
to warp grids and images.
- traveling salesman problem
-
This is a classic
tour problem in which a hypothetical salesman must
find the most efficient sequence of destinations in his territory,
stopping only once at each.
- trusted login
-
A user is said to have a
trusted login to another computer when that user is not prompted for a
password when accessing the remote computer.
- tuple
-
A row in a relational
table; synonymous with record, observation.
-
A turn represents a
transition from one
network link to another at a
network node. Turns represent relationships between network links
rather than an abstraction of some real-world physical entity. The
properties of a turn are stored in a turntable.
-
The impedance or cost of
making a turn at a network node. A turn impedance for
making a left turn can be different from that of a right turn or a U-turn
at a node.
-
An INFO file containing the
turn impedances between pairs of network links.
There can be sixteen possible turn impedances between four network links
meeting at a node (i.e., left, right, straight, and U-turn for each of the
four network links).
- undershoot
-
An arc that does not extend
far enough to intersect another arc. See also
dangling arc.
-
A
topological overlay of two polygonal spatial data sets which preserves
features that fall within the spatial extent of either input data set;
that is, all features from both coverages are retained. See also
intersect and
identity.
- Universal Transverse Mercator (UTM)
-
A system of plane
coordinates based upon 60 north-south trending zones, each 6 degrees of
longitude wide, that circle the globe. Used to derive geographic
coordinates, normally in meters, east and north of an origin that are
defined uniquely grid for each zone.
-
The first record in a
polygon attribute table. It represents the area beyond the outer boundary
of the coverage. It's the only polygon that never has a label point, and
so has a User-ID value of 0. Its area equals the negative sum of all the
polygons in the coverage. Also referred to as the external polygon.
- UNIX
-
A modern, general purpose
operating system.
- upstream
-
In tracing, upstream is the
direction along the arcs that is against the direction of flow. Direction
of flow is determined by a user-defined convention. See
directed network.
- User-ID
-
Synonymous term for
Cover-ID and feature-ID.
- user interface
-
Method by which the human
operator communicates with the various database, system, and applications
modules.
- USGS DEM
-
A digital elevation model
produced by the Survey Branch of the United States Department of the
Interior, consisting of a regular array of elevations referenced in the
Universal Transverse Mercator (UTM) coordinate system. These data
correspond to the standard 1:24,000-scale 7.5 x 7.5-minute quadrangles or
1:250,000 one-degree map sheets. Elevations are in meters or feet
referenced to mean sea level.
- USNMAS
-
U.S. National Map Accuracy
Standards: Accuracy standards for published maps in English units defining
measurements for horizontal and vertical accuracy. It is described in
absolute terms; however, it is not described in statistical terms and some
inconsistencies have been noted, thereby making it unusable for
engineering mapping (large-scale mapping), and is not convenient to use in
conjunction with mapping from space (remote sensing).
- utility mapping
-
A special class of GIS
applications for managing information about public utilities such as water
pipes, sewerage, telephone, electricity, and gas networks.
-
Value attribute table. A
table containing attributes for a
grid.
In addition to user-defined attributes, the VAT contains the values
assigned to cells in the grid and a count of the cells with those values.
-
A coordinate-based data
structure commonly used to represent linear geographic features. Each
linear feature is represented as an ordered list of
vertices. Traditional vector data structures include double-digitized
polygons and arc-node models.
-
One of a set of ordered x,y
coordinates that constitutes a line.
- virtual table
-
See view.
-
A logical table whose data
are not physically stored. You define a view to access a subset of the
columns stored in a row, access a set of columns stored in different rows,
or avoid creating a redundant copy of data that is already stored.
- viewshed modeling
-
See intervisibility
functions.
- VPF
-
Vector product format is a
digital geographic vector-based format used by the U.S. Defense Mapping
Agency for the distribution of its vector data sets. ArcInfo includes a
bidirectional VPF translator.
- VRF
-
Vector relational format. A
relational model-based format very similar to the DMA VPF (Defense Mapping
Agency Vector Product Format).
- WAIS
-
Wide-Area Information
Server. A client/server software system that provides sophisticated
indexing of files based on all words in each file and provides scoring and
"relevance feedback" of documents to its client. The client then selects
which file or files to retrieve from the server from a list of file or
document titles, ranked by a score assigned by the software. Searching can
include Boolean constructs and access to structured information systems
(like databases) through its compliance with ANSI standard Z39.50. WAIS is
addressed at the operating system level.
-
Wide area network. Computer
data communications technology that connects computers at remote sites.
WANs are composed of special data communications hardware and software and
usually operate across public or dedicated telephone networks.
- warping
-
See rubber sheeting.
- watch file
-
A text file that records
all nongraphic input and output during an ArcInfo session. Watch files can
be edited and converted to
AML
programs.
- wavelength
-
In general, the mean
distance between two adjacent “crests” (or “troughs”) of a periodic
pattern. The smaller the wavelength becomes the greater the intensity of
energy. Wavelength = velocity / frequency..
- weed tolerance
-
The minimum allowable
distance between any two vertices along an arc. Weed tolerance is a
parameter that can be set before adding arc features. When adding new
arcs, if an input vertex is within the weed distance of the last vertex,
it is disregarded. When weeding existing arcs, it is the tolerance used by
the Douglas-Peucker algorithm. Nodes are always retained. The proximity of
vertices on one arc to vertices on another arc within the tolerance does
not cause them to be weeded; this is controlled by the
proximal tolerance.
- workspace
-
A directory containing
geographic data sets for use with ArcInfo. A workspace contains an INFO
directory for the feature attribute tables. ArcInfo workspaces have three
primary uses: as a user work area, to store all the map sections for each
tile in a map library, and as automation workspaces to store all the
versions of a single coverage as it progresses through the coverage
automation process.
- workstation
-
1. The desk, keyboard,
digitizing table, and CRTs connected together as a unit for working with
maps or graphics in interactive GIS and CAD/CAM. 2. A computer that
consists of a graphic terminal, central processor, digitizer, graphics
tablet (optional), and a mouse (optional). It may also be a stand-alone
central processing unity (CPU) and its peripheral devices. It is often
linked to other computers through a network.
- World Wide Web
-
Developed by the European
Laboratory for Particle Physics (CERN)
- (WWW)
-
Consortium in Switzerland
as a distributed hypermedia server. It allows one to prepare electronic
documents that are composites of, or pointers to, many different files of
potentially different types scattered across the world. It employs a
hypertext markup language (html) to create the documents it serves and to
follow "links" known as Universal Resource Locators (URLs) to fetch the
document from elsewhere on the Internet. A WWW server does not provide
search capabilities, rather it provides explicit linkage between files on
the Internet using hypertext. This allows one to organize information in a
particular way, but, unless the links exist, does not permit the discovery
of other information that was not associated by the author. WWW can be
accessed by Mosaic (see
Mosaic).
- X Windows
-
A system developed at MIT
that allows applications to be displayed in windows and shared among
different workstations and terminals. Available on all UNIX operating
systems supported by ArcInfo and ArcView. ArcInfo and ArcView are X
Windows-based applications. ArcInfo or ArcView can be run on any
X-compliant terminal or X Station on all supported UNIX platforms or on
any PC or Macintosh through emulation software.
- X Windows/Motif
-
ArcInfo and ArcView operate
in the X Windows/Motif environment on all supported UNIX workstation
platforms.
- X.25
-
CCITT recommendation/ISC standard for wide area networks.
- X.400
-
ISO standard for electronic
mail.
- X-Open Consortium
-
An association of American
and European vendors formed in 1984 to promote open systems.
- XPG3
-
An X/Open software standard
for UNIX Operating Systems. IBM provides a cshell variable named PSALLOC
to make AIX XPG3-compliant, resulting in adding more swap space on disk,
protects ArcInfo from an outside application bug-induced crash, and
increases application performance.
- Z39.50
-
An ANSI protocol standard
for WAN (wide area network) information query and exchange to share
library referencing requests via distributed electronic access to
information.
- z-value
-
The value of a surface at a
particular x,y location (e.g., elevation). Often referred to as spot
values or spot elevations.
-
To enlarge and display
greater detail of a portion of a geographic data set.