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A B C D
E F G H
I J K L
M N O P
Q R S T
U V W X
Y Z
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A
address matching
A mechanism for relating two files using address as the relate item.
Geographic coordinates and attributes can be transferred from one address to the
other. For example, a data file containing student addresses can be matched to a
street coverage that contains addresses creating a point coverage of where the
students live.
annotation
1. Descriptive text used to label coverage features. It is used for display,
not for analysis.
2. One of the feature classes in a coverage used to label other features. Information stored for annotation includes a text string, the location at which it is displayed, and a text symbol (color, font, size, etc.) for display.
arc
1. An ordered string of vertices (x,y coordinate pairs) that begin at one
location and end at another. Connecting the arc's vertices creates a line. The
vertices at each endpoint of an arc are called nodes.
area
1. A homogeneous extent of the Earth bounded by one or more arc features or
represented as a set of polygons. Examples: states, counties, lakes, land-use
areas, and census tracts.
2. The size of a geographic feature measured in unit squares. ArcInfo stores an
area measure for each polygon and region.
attribute
1. A characteristic of a geographic feature described by numbers, characters,
images and CAD drawings, typically stored in tabular format and linked to the
feature by a user-assigned identifier (e.g., the attributes of a well might
include depth and gallons per minute).
2. A column in a database table.
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buffer
A zone of a specified distance around coverage features. Both constant- and variable-width buffers can be generated for a set of coverage features based on each feature's attribute values. The resulting buffer zones form polygons-areas that are either inside or outside the specified buffer distance from each feature. Buffers are useful for proximity analysis (e.g., find all stream segments within 300 feet of a proposed logging area).
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CAD
Computer-aided design. An automated system for the
design, drafting, and display of graphically oriented information.
clip
The spatial extraction of those features from one
coverage that reside entirely within a boundary defined by features in another
coverage (called the clip coverage)-clipping works much like a cookie cutter.
coordinate system
A reference system used to measure horizontal and
vertical distances on a planimetric map. A coordinate system is usually defined
by a map projection, a spheroid of reference, a datum, one or more standard
parallels, a central meridian, and possible shifts in the x- and y-directions to
locate x,y positions of point, line, and area features. In ArcInfo, a system
with units and characteristics defined by a map projection. A common coordinate
system is used to spatially register geographic data for the same area.
coverage
1. A digital version of a map forming the basic unit of
vector data storage in ArcInfo. A coverage stores geographic features as primary
features (such as arcs, nodes, polygons, and label points) and secondary
features (such as tics, map extent, links, and annotation). Associated feature
attribute tables describe and store attributes of the geographic features.
2. A set of thematically associated data considered as a
unit. A coverage usually represents a single theme such as soils, streams,
roads, or land use.
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database
A logical collection of interrelated information, managed
and stored as a unit, usually on some form of mass-storage system such as
magnetic tape or disk. A GIS database includes data about the spatial location
and shape of geographic features recorded as points, lines, areas, pixels, grid
cells, or tins, as well as their attributes.
data dictionary
A catalog of all data held in a database, or a list of
items giving data names and structures. Also referred to as DD/D for data
dictionary/directory. Commercial RDBMSs have online data dictionaries stored in
special tables called system tables.
database
management system (DBMS)
A set of computer programs for organizing the information
in a database. A DBMS supports the structuring of the database in a standard
format and provides tools for data input, verification, storage, retrieval,
query, and manipulation.
datum
A set of parameters and control points used to accurately
define the three-dimensional shape of the Earth (e.g., as a spheroid). The datum
is the basis for a planar coordinate system. For example, the North American
Datum for 1983 (NAD83) is the datum for map projections and coordinates within
the United States and throughout North America.
digitize
1. To encode geographic features in digital form as x,y
coordinates.
2. The process of using a digitizer to encode the
locations of geographic features by converting their map positions to a series
of x,y coordinates stored in computer files. Pushing a digitizer button records
an x,y coordinate. A digitized line is created by recording a series of x,y
coordinates.
dissolve
The process of removing boundaries between adjacent
polygons that have the same values for a specified attribute.
double precision
Refers to a high level of coordinate accuracy based on
the possible number of significant digits that can be stored for each
coordinate. ArcInfo data sets can be stored in either single- or
double-precision coordinates. Double-precision coverages store up to 15
significant digits per coordinate (typically, 13 to 14 significant digits),
retaining the accuracy of much less than one meter at a global extent. See also
single precision.
DXF
Data Exchange Format. A format for storing vector data in
ASCII or binary files. Used by AutoCAD and other CAD software for data
interchange. DXF files are convertible to ArcInfo coverages.
dynamic
segmentation
The process of computing the locations of events on
linear features at run time based on event tables for which distance measures
are available. Route-system features and event-handling commands provide the
dynamic segmentation capability within ArcInfo.
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edge matching
An editing procedure to ensure that all features that
cross adjacent map sheets have the same edge locations. Links are used when
matching features in adjacent coverages.
edit
To correct errors within, or modify, a computer file, a
geographic data set, or a tabular file containing attribute data.
environment
A set of parameters defining various display, editing,
and data manipulation conditions that remain active during a session until
explicitly changed by the user. For example, the drawing environment in ARCEDIT
might be 'arcs on, labels off, annotation.streets on'.
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feature class
1. A classification describing the format of geographic
features and supporting data in a coverage. Coverage feature classes for
representing geographic features include point, arc, node, route-system, route,
section, polygon and region. One or more coverage features are used to model
geographic features; for example, arcs and nodes can be used to model linear
features such as street centerlines. The tic, annotation, link, and boundary
feature classes provide supporting data for coverage data management and
viewing.
2. The conceptual representation of a geographic feature.
When referring to geographic features, feature classes include point, line,
area, and surface.
field
In a database, another term for column.
file
A set of related information that a computer can access
by a unique name (e.g., a text file, a data file, a DLG file). Files are the
logical units managed on disk by the computer's operating system. Files may be
stored on tapes or disks.
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geocode
The process of identifying the coordinates of a location
given its address. For example, an address can be matched against a TIGER street
network to determine the location of a home. Also referred to as address
geocoding.
geographic
database
A collection of spatial data and related descriptive data
organized for efficient storage and retrieval by many users.
georeference
To establish the relationship between page coordinates on
a planar map and known real-world coordinates.
GIS
Geographic information system. An organized collection of
computer hardware, software, geographic data, and personnel designed to
efficiently capture, store, update, manipulate, analyze, and display all forms
of geographically referenced information.
global positioning
system
A system of satellites and receiving devices used to
compute positions on the Earth. GPS is used in navigation, and its precision
supports cadastral surveying.
graphical user
interface (GUI)
A graphical method of controlling how a user interacts
with a computer to perform various tasks. Instead of issuing commands at a
prompt, the user performs desired tasks by using a mouse to choose from 'a
dashboard' of options presented on the display screen. These are in the form of
pictorial buttons (icons) and lists. Some GUI tools are dynamic and the user
must manipulate a graphical object on the screen to invoke a function; for
example, moving a slider bar to set a parameter value (e.g., setting the scale
of a map).
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hardware
The physical components of a computer system-the
computer, plotters, printers, terminals, digitizers, and so on.
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identity
The topological overlay (input) with a polygon coverage
(identity). For each feature in the input coverage, the intersection with
identity features is determined, creating new features of the same feature class
as the input coverage. For example, a road (input coverage, arc feature class)
passing through two counties (identity coverage) would be split into two arc
features, each with the attributes of the road and the county it passes through.
Compare with intersect and union.
index
Special data structure used in a database to speed
searching for records in tables or spatial features in geographic data sets.
ArcInfo supports both spatial and attribute indexes.
See also item indexing, cross-tile indexing and spatial indexing.
intersect
The topological integration of two spatial data sets
that preserves features that fall within the area common to both input data
sets. See also identity and union.
item
A column of information in an attribute table, for
example, a single attribute of a record in an INFO data file.
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latitude-longitude
A spherical reference system used to measure locations
on the Earth's surface. Latitude and longitude are angles measured from the
Earth's center to locations on the Earth's surface. Latitude measures angles in
a north-south direction. Longitude measures angles in the east-west direction.
layer
A thematic set of spatial data described and stored in
an ArcStorm database or a LIBRARIAN map library. Layers organize a database or
map library by subject matter (e.g., soils, roads, and wells). Conceptually,
layers in a database or map library environment are exactly like coverages. See
also ArcStorm database and map library.
legend
1. The reference area on a map that lists and explains
the colors, symbols, line patterns, shadings, and annotation used on the map.
The legend often includes the scale, origin, orientation, and other map
information.
2. The symbol key used to interpret a map.
line
1. A set of ordered coordinates that represents the
shape of geographic features too narrow to be displayed as an area at the given
scale (e.g., contours, street centerlines, or streams), or linear features with
no area (e.g., state and county boundary lines).
2. A single arc in a coverage.
3. A line on a map (e.g., a neatline).
line symbol
A symbol for drawing coverage arcs.
link
A coverage feature class; links are two-point segments
that represent from- and to-locations for the rubber sheeting adjustment
process.
lookup table
1. A special tabular data file containing additional
attributes for features stored in an associated feature attribute table. The
table can be an external attribute table or an INFO table that describes
coverage features.
2. A special lookup table in which numeric item values
are classified into categories. For example, well depth can be recorded
explicitly in the feature attribute table, but displayed and used as a set of
classes, such as 0 to 250 feet, 251 to 500 feet, and so on. An INFO lookup table
contains at least two items: the relate item and an item named either SYMBOL or
LABEL.
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map
An abstract representation of the physical features of a portion of the
Earth's surface graphically displayed on a planar surface. Maps display signs,
symbols, and spatial relationships among the features. They typically emphasize,
generalize, and omit certain features from the display to meet design objectives
(e.g., railroad features might be included in a transportation map but omitted
from a highway map).
map extent
1. The rectangular limits (xmin,ymin and xmax,ymax) of the area of the Earth's
surface displayed using ArcInfo. Map extent is specified in the coordinate
system of the coverage or other geographic data set used. Typically, the extent
of the geographic database (or a portion of it defined by a zoomed-in view)
defines the map extent for display.
2. The geographic extent of a geographic data set specified by the minimum
bounding rectangle (i.e., xmin,ymin and xmax,ymax).
map limits
The rectangular area on the graphics page in which geographic features are
displayed. All geographic data are drawn within the map limits, and none outside
the map limits. Map titles and legends can be drawn outside the map limits.
map scale
The reduction needed to display a representation of the Earth's surface on a
map. A statement of a measure on the map and the equivalent measure on the
Earth's surface, often expressed as a representative fraction of distance, such
as 1:24,000 (one unit of distance on the map represents 24,000 of the same units
of distance on the Earth). Map scale can also be expressed as a statement of
equivalence using different units; for example, 1 inch = 1 mile or 1 inch =
2,000 feet.
map units
The coordinate units in which a geographic data set (e.g., a coverage) is stored
in ArcInfo. Map units can be inches, centimeters, feet, meters, or decimal
degrees.
marker symbol
A symbol used to represent a point location such as an airport.
MrSID
MrSID is a unique raster file format developed by
LizardTech to encode large, high-resolution images to a fraction of their
original size while maintaining the original image quality
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node
1. The beginning and ending locations of an arc. A node is topologically linked
to all arcs that meet at the node. See also network node.
2. In graph theory, the location at which three or more lines connect.
3. The three corner points of each triangle in a tin. Every sample point
input to a tin becomes a node in the triangulation. A triangle node is
topologically linked to all triangles that meet at the node.
node match tolerance
The minimum radial distance within which two nodes will be joined (matched) to
form one node.
null value
The absence of a value. If a particular column of a row in a table is null, that
means there is no value stored. Null is not the same as blank or zero.
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ODBC
Open Database Communication. A standard API (application program interface) used
to communicate with database management systems, developed by Microsoft, and
incorporated in ArcView Version 2. ArcView supports ODBC for DBMSs on the
Microsoft Windows platform.
OLE
Object Linking and Embedding developed by Microsoft. Allows objects from one
application to be embedded within another (e.g., taking an Excel
spreadsheet and putting it into a Word document). ArcView Version 2 does not
support the still evolving OLE standard. Instead, it supports DDE (see DDE).
OLE support is planned for future releases of ArcView.
one-to-many
A relate in which one record in a table is related to many records in another
table.
overlay
A topological
overlay procedure which determines the spatial coincidence of two sets of
polygon features and creates a new set of polygons based on identity, intersect,
or union.
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page extent
Defines a rectangular portion of the graphics
page to be displayed.
pan
To move the viewing window up, down, or sideways to display areas in a
geographic data set which, at the current viewing scale, lie outside the viewing
window. See also zoom.
polygon
A coverage feature class used to represent areas.
A polygon is defined by the arcs that make up its boundary and a point
inside its boundary for identification. Polygons have attributes (PAT)
that describe the geographic feature they represent.
polygon-arc topology
The topological data structure ArcInfo uses to represent connectivity between
arcs to form polygons. Polygon-arc topology supports the definition of polygons
and analysis functions such as topological
overlay. See also topology.
precision
Refers to the number of significant digits used to store numbers, and in
particular, coordinate values. Precision is important for accurate feature
representation, analysis and mapping. ArcInfo supports single
precision and double
precision.
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raster
A cellular data structure composed of rows and columns for storing images.
Groups of cells with the same value represent features.
RDBMS
Relational database management system. A database management system with the
ability to access data organized in tabular files that can be related to each
other by a common field (item). An RDBMS has the capability to recombine the
data items from different files, providing powerful tools for data usage. See
also relate.
record
1. In an attribute table, a single 'row' of thematic descriptors. In SQL terms,
a record is analogous to a tuple.
2. A logical unit of data in a file. For example, there is one record in the
ARC file for each arc in a coverage.
relate
An operation that establishes a temporary connection between corresponding
records in two tables using an item common to both (i.e., relate key). Each
record in one table is connected to those records in the other table that share
the same value for the common item. Compare with relational
join.
relational database
A method of structuring data as collections of tables that are logically
associated to each other by shared attributes. Any data element can be found in
a relation by knowing the name of the table, the attribute (column) name, and
the value of the primary key. See also relate, relate
key, and relational join.
relational join
The operation of relating and physically merging two attribute tables using
their common item.
row
1. A record in an attribute table. The horizontal dimension of a table composed
of a set of columns containing one data item each.
2. A horizontal group of cells in a grid, or pixels in an image.
rubber sheeting
A procedure to adjust coverage features in a nonuniform manner. Links
representing from- and to-locations are used to define the adjustment.
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scale bar
A map element that shows the map scale graphically.
scanning
The process of capturing data in raster format with a
device called a scanner. Some scanners also use software to convert raster data
to vector data.
shade symbol
A pattern used to shade polygons in ArcInfo. Shade symbol patterns include
crosshatch, repeating, and solid fill.
sliver polygon
A small areal feature commonly occurring along the borders of polygons following
the topological
overlay of two or more coverages.
snapping
The process of moving a feature to coincide exactly with coordinates of another
feature within a specified snapping distance, or tolerance.
spatial analysis
The process of modeling, examining, and interpreting model
results. Spatial analysis is useful for evaluating suitability and capability,
for estimating and predicting, and for interpreting and understanding. There are
four traditional types of spatial analysis: topological
overlay and contiguity analysis, surface analysis, linear analysis, and
raster analysis.
spatial data
Information about the location and shape of, and relationships among, geographic
features, usually stored as coordinates and topology.
SQL
Structured Query Language. A syntax for defining and manipulating data from a
relational database. Developed by IBM in the 1970s, it has become an industry
standard for query languages in most relational database management systems.
string
A series of alphanumeric characters of any length enclosed by quotes.
symbol
A graphic pattern used to represent a feature. For example, line symbols
represent arc features; marker symbols, points; shades symbols, polygons; and
text symbols, annotation. Many characteristics define symbols, including color,
size, angle, and pattern. See also text symbol, marker
symbol, shade symbol, and line
symbol.
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table
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.
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.
text symbol
A text style defined by font, size, character spacing, color, and so on, used to
label maps and coverage features in ArcInfo.
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.
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.
topographic map
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.
topology
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.
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.
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union
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.
universe polygon
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.
vector
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.
vertex
One of a set of ordered x,y coordinates that constitutes a line.
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.
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zoom
To enlarge and display greater detail of a portion of a geographic data set.
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| This page was last modified on December 21, 2006 |
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