AAT Arc Attribute Table. A table
containing attributes for a line coverage such as
streets or streams.
absolute The accuracy of a map in
representing the geographic location of an object
relative to its true location on the surface of the
Earth. Absolute accuracy is based on geographic
The accuracy of a map in representing the geographic
location of an object relative to the locations of
AM/FM Automated Mapping and
Facilities Management. The management of mapping and
facilities management using integrated computer
AML The ARC Macro Language. A high
level language that provides full programming
capabilities and a set of tools for building menus to
tailor user interfaces for specific applications.
annotation Descriptive text used to label
arc A string of x,y coordinate
pairs (vertices) that begin at one location and end
at another. Connecting the arc's vertices creates a
attribute A characteristic of a
geographic feature described by numbers or letters,
typically stored in tabular format and linked to the
feature in a relational database. The attributes of a
well represented by a point might include depth,
location, and permit number.
base map A map containing visible
surface features and boundaries, essential for
locating additional layers, or types, of
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 features attribute values.
CAD Computer Aided Design. An
automated system for the design, drafting and display
of graphically oriented information.
cadastre Public record of the extent,
value and ownership of land within a district for
purposes of taxation.
Coordinate System A two dimensional
coordinate system in which x measures horizontal
distance and y measures vertical distance. An x,y
coordinate defines every point on the plane.
clip The spatial extraction of
those features from one coverage that reside entirely
within the boundary defined by features in another
coverage. Clipping works much like a cookie cutter.
COGO Abbreviation for the term
COordinate GeOmetry. Land surveyors use COGO
functions to enter survey data, to calculate precise
locations and boundaries, to define curves, and so
contour line An imaginary line joining
points of equal elevation.
control points A set of points on the ground
whose horizontal and vertical location is known.
Control points are used as the basis for detailed
coordinate An x,y location in a Cartesian
coordinate system or an x,y,z coordinate in a three
dimensional system. Coordinates represent locations
on the Earth's surface relative to other locations.
coverage A digital version of a map
forming the basic unit of vector data storage in
ARC/INFO. A coverage stores map 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
map features. A coverage usually represents a single
theme, or layer, such as soils, roads, or land use.
coverage units The units (e.g., feet, meter,
inches) of the coordinate system in which a coverage
data conversion The translation of data from
one format to another. ARC/INFO supports data
conversion from many different geographic data
formats in addition to routines for converting paper
maps. Those data formats include DLG, TIGER, DXF, and
database A logical collection of
interrelated information, managed and stored as a
unit. A GIS database includes data about the spatial
location and shape of geographic features recorded as
points, lines, and polygons as well as their
datum A set of parameters and
control points used to accurately define the three
dimensional shape of the Earth. The corresponding
datum is the basis for a planar coordinate system.
For example the North American datum, 1927 is the
datum for coordinates used in Volusia County's GIS.
DBMS Data Base Management System.
Software that manages, manipulates and retrieves data
in a database.
DGPS Differential Global
Positioning System. A positioning procedure that uses
two receivers, a rover at an unknown location and a
base station at a known, fixed location. The base
station computes corrections based on the differences
between its actual and observed ranges to the
satellites being tracked.
library A series of directories and
subdirectories designed to uniformly organize a
collection of spatial data. Map libraries organize
geographic data spatially as a set of tiles and
thematically as a set of layers. Volusia
County's digital map library is divided into large scale and small
scale subdirectories containing several hundred tiles
comprising 90 layers of information.
Elevation Model (DEM) Terrain
elevation data organized by quadrangle and provided in digital form.
Terrain Model (DTM) A
three-dimensional model of the Earth's surface,
provided in digital form.
digitize To encode map features as x,y
coordinates in digital form. Lines are traced to
define their shapes. This can be accomplished either
manually or by use of a scanner.
dissolve The process of removing
boundaries between adjacent polygons that have the
same values for a specified attribute.
DLG Digital Line Graph files from
the U.S. Geological Survey.
DXF Data Exchange Format. A format
for storing vector data in ASCII or binary files;
used by AutoCad or other CAD software and convertible
to ARC/INFO coverages.
edge matching An editing procedure to ensure
that all features that cross adjacent map sheets have
the same edge locations.
ethernet A baseband protocol invented by
the Xerox Corporation in common use as the local area
network for UNIX operating systems interconnected by
TCP/IP. Runs at 16 megabits per second.
attribute table A table used by ARC/INFO to
store attribute information for a specific coverage
feature class. Feature attribute tables supported
Cover.PAT for polygons or points
Cover.AAT for arcs
Cover.NAT for nodes
Cover.RAT for routes
Cover.SEC for sections
Cover.TAT for annotation(text)
- where "Cover" is the coverage name
feature class The type of feature
represented in a coverage. Coverage feature classes
include arcs, nodes, label points, polygons, tics,
annotation, links, boundaries, routes, and sections.
geocode The process of identifying a
location by one or more x,y coordinates from another
location description such as an address. For example,
an address can be matched against Volusia County's
street centerline file to determine an x,y
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
Positioning System (GPS) A satellite
based device that records x,y,z coordinates and other
data. GPS devices can be taken into the field to
record data while driving, hiking, or flying. Ground
locations are calculated by signals from satellites
orbiting the Earth.
INFO A tabular DBMS used by
ARC/INFO to store and manipulate feature attribute
and related tables.
intersect The topological integration of
two spatial data sets that preserves features that
fall within the spatial extent common to both input
item In an attribute table, a field
of information commonly displayed as a column. A
single attribute from a record in an INFO data file.
latitude-longitude A spherical reference system
used to measure locations on surface. Latitude
measures angles in the north south direction and
longitude measures angles in the east west direction.
layer A logical set of thematic data
described and stored in a map library. Layers
organize a map library by subject matter, e.g.,
soils, roads, wells, and extend over the entire
geographic area defined by the spatial index of the
line-in-polygon A spatial operation in which
arcs in one coverage are overlaid with polygons in
another to determine which arcs, or portions of arcs,
are contained within the polygons. Polygon attributes
are associated with corresponding arcs in the
resulting line coverage.
logical selection The process of selecting a
subset of features from a coverage using logical
selection criteria that operate on the attributes of
coverage features (e.g., area greater than 16,000
square feet). Only those features whose attributes
meet the selection criteria are selected. Also known
as feature selection by attribute.
many-to-one-relate A relate in which many records
in one table are related to a single record in
another table. A goal in relational database design
is to use one to many relates to reduce data storage
map extent The rectangular limits
(xmin,ymin,xmax,ymax) of the area of the Earth's
surface you want to display using ARC/INFO. The
geographic extent specified by the minimum bounding
rectangle of a study area.
map projection A systematic conversion of
locations on the Earth's surface from spherical to
planar coordinates. Several of the more popular
projections are: State Plane Coordinates (SPC) which
uses feet for units of measure; Universal Transverse
Mercator (UTM) which uses meters for units of
measure; and latitude and longitude which uses
degrees, minutes, and seconds of arc for units of
map scale The extent of 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 in the map equals 24,000
units on the ground).
one-to-many-relate A type of relate connecting a
unique value in one file to many records (that have
the same value) in another file.
orthophotography The process of aerial
photographs that have been rectified to produce an
accurate image of the Earth by removing tilt and
relief displacements which occurred when the photo
PAT Point Attribute Table. Polygon
Attribute Table. A coverage can have either a point
attribute table or a polygon attribute table, but not
photogrammetry The science of deducing the
physical dimension of objects from measurements on
planimetric The horizontal (x,y) locations
of non-topographic features, such as rivers, lakes,
buildings, roads, etc.
point-in-polygon A spatial operation in which
points from one coverage are overlaid with a
polygonal coverage to determine which points fall
within the polygon boundaries. Points assume the
attributes of the polygons within which they fall.
polygon A multisided figure that
represents area on a map. A feature defined by the
arcs that make up its boundary. Every polygon
contains one label point within its boundary.
Polygons have attributes that describe the geographic
feature they represent.
polygon overlay A process that merges
spatially coincident polygons from two coverages, and
their attributes, to create a third coverage, that
contains new polygons and describes new
to a map sheet published by the U.S. Geological
Survey, a 7.5 minute quadrangle series or the 15
minute quadrangle series. Also known as a topographic
or topo map.
raster Data displayed as discrete
picture elements (pixels).
relate An operation that establishes
a temporary connection between corresponding records
in two tables using an item common to both. A relate
gives access to additional feature attributes that
are not stored in a single table.
relate key The common set of columns used
to relate two attribute tables.
remote sensing Any of the technical
disciplines for observing and measuring the Earth
from a distance, including satellite imaging, Global
Positioning Systems, RADAR, SONAR, aerial
resolution Measures the sharpness of an
Availability (S/A) A U.S.
Department of Defense program to limit the accuracy
of autonomous position fixes computed by civilian
receivers. The error in position caused by S/A can be
up to 100 meters.
slope A measure of change in surface
value over distance, expressed in degrees or as a
percentage. For example, a rise of 2 meters over
distance of 100 meters describes a 2% slope.
spatial analysis The process of modeling,
examining, and interpreting model results. Spatial
analysis is the process of extracting or creating new
information about a set of geographic features.
Spatial analysis is useful for evaluating suitability
and capability, for estimating and predicting, and
for interpreting and understanding. In GIS there are
four traditional types of spatial analysis: spatial
overlay and contiguity analysis, surface analysis,
linear analysis, and raster analysis.
spatial modeling Analytical procedures applied
with GIS. There are three categories of spatial
modeling functions that can be applied to geographic
data within a GIS: geometric models, such as
calculating the distance between features, generating
buffers, calculating areas and perimeters, and so on;
coincidence modeling, such as polygon overlay; and
adjacency modeling such as redistricting and
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
Coordinates (SPC) A map projection that
measures distance in feet. By providing an SPC
easting (x) and northing (y), the state name, and the
zone number, any location in the United States can be
identified by a unique coordinate value. SPC Zone
boundaries follow state and county boundaries.
Florida, due to its size and shape is divided into
three SPC zones, north, east, and west. Volusia
County is entirely within the East Zone. State Plane
Coordinates are admirably suited to the needs of the
local land surveyor and are widely used for public
works, land surveys, and for Geographic Information
TIN Triangulated Irregular Network.
A series of triangles constructed using elevation
data points taken from coverages. These triangles are
used for surface representation and display.
topography Shape or configuration of the
land surface; represented in map form by contour
topology The spatial relationships
between connecting or adjacent coverage features.
transformation The process that converts
coordinates from one coordinate system to another
through translation, rotation, and scaling.
triangulation A method of surveying in the
location of an object may be calculated from the
known locations of two other objects. Creating a
triangle from the three items, the angles and sides
of the triangle can be measured and the location of
the unknown object is calculated algebraically.
vector A geometric element, stored as
a point with x,y coordinates within a computer