active data: Data that can be reconfigured
and recomputed in place. Spreadsheet term for data for attributes or records
created by formulas within a spreadsheet.
address matching: Address matching means
using a street address such as 123 Main Street in conjunction with a
digital map to place the street address onto the map in a known location. Address
matching a mailing list, for example, would convert the mailing list to a map
and allow the mapping of characteristics of the places on the list.
affine transformation: Any set of translation,
rotation, and scaling operations in the two spatial directions of the plane.
Affine transformations allow maps with different scales, orientations, and origins
to be coregistered.
AutoCAD® Map: A GIS software package.
See Section 8.5.
batch: Submission of a set of commands
to the computer from a file rather than directly from the user as an interactive
big eight: The eight most popular GIS
packages, established by the number of users, particularly among people getting
started with GIS, at any given time.
buffer: A zone around a point, line,
or area feature that is assumed to be spatially related to the feature.
CALFORM: An early computer mapping package
for thematic mapping.
CAM (Computer-Assisted Mapping): A map
projection and outline plotting program for mainframe computers dating from
CGIS (Canadian Geographic Information System):
An early national land inventory system in Canada that evolved into a full GIS.
clump: To aggregate spatially; to join
together features with similar characteristics into a single feature.
compression: Any technique that reduces
the physical file size of data in a spatial or other data format.
cookie-cut: A spatial operation to exclude
area outside a specific zone of interest. For example, a state outline map can
be used to cut out pixels from a satellite image.
critical six: The GIS functional capabilities
included in Duekers GIS definition: map input, storage, management, retrieval,
analysis, and display.
data exchange format: The specific physical
data format in which exchange of data between similar GIS packages takes place.
data structure: The logical and physical
means by which a map feature or an attribute is digitally encoded.
DBMS (Database Management System):
Part of a GIS, the set of tools that allows the manipulation and use of files
containing attribute data.
desktop mapping: The ability to generate
easily a variety of map types, symbolization methods, and displays by manipulating
the cartographic elements directly.
desktop metaphor: For a GUI, the physical
analogy for the elements with which the user will interact. Many computer GUIs
use the desktop as a metaphor, with the elements of a calendar, clock, files
and file cabinets, and so on.
device independence: The ability of software
to run with little difference from a users perspective on any computer or on
any specialized device, such as a printer or plotter.
dissolve: Eliminating a boundary formed
by the edge or boundary of a feature that becomes unnecessary after data have
been captured: for example, the edges of sheet maps.
Duekers definition of GIS: "A special
case of information systems where the database consists of observations on spatially
distributed features, activities or events, which are definable in space as
points, lines, or areas. A geographic information system manipulates data about
these points, lines, and areas to retrieve data for ad hoc queries and analyses."
DXF: AutoCADs® digital file exchange
format, a vector-mode industry standard format for graphic file exchange.
dynamic segmentation: GIS function that
breaks a line into points at locations that have significance, and that can
have their own attributes. For example, the line representing a highway can
have a new node added every mile as a mile marker that can hold attributes about
the traffic flow at that place.
entity by entity: Any data structure
that specifies features one at a time, rather than as an entire layer.
FORTRAN: An early computer programming
language, initially for converting mathematical formulas into computer instructions.
functional capability: One of the distinctive
processes that a GIS is able to perform as a separate operation or as part of
functional definition: Definition of
a system by what it does rather than what it is.
fuzzy tolerance: Linear distance within
which points should be snapped together.
generalization: The process of moving
from one map scale to a smaller (less detailed) scale, changing the form of
features by simplification, and so on.
geometric test: A test to establish the
spatial relationship between features. For example, a point feature can be given
a point-in-polygon test to find if it is "contained" by an area.
GNU: Free Software Foundation organization
that distributes software over the Internet.
GRASS: A GIS software package (see Section
GUI (Graphical User Interface): The set
of visual and mechanical tools through which a user interacts with a computer,
usually consisting of windows, menus, icons, and pointers.
help line: A telephone service available
to software users for verbal help from an expert.
import: The capability of a GIS to bring
data in an external file and in a nonnative format for use within the GIS.
installation: The step necessary between
delivery of GIS software and its first use, consisting of copying and decompressing
files, data, registering licenses, and so on.
integrated software: Software that works
together as part of a common user interface rather than software that consists
of separate programs to be used in sequence.
local area network: An arrangement of
computers into a cluster, with network linkages between computers but no external
link. Usually, this allows sharing data and software licenses, or the use of
a file server.
macro: A command language interface allowing
a "program" to be written, edited, and then submitted to the GIS user
map algebra: Tomlins terminology for
the arithmetic of map combination for coregistered layers with rasters of identical
size and resolution.
map overlay: Placing multiple thematic
maps in precise registration, with the same scale, projections, and extent,
so that a compound view is possible.
Maptitude: A GIS software package (see
mask: A map layer intended to eliminate
or exclude areas not needed for mapping and analysis.
metadata: Data about data. Index-type
information pertaining to the entire data set rather than the objects within
the data set. Metadata usually includes the date, source, map projection, scale,
resolution, accuracy, and reliability of the information, as well as data about
the format and structure of the data set.
mosaic: The GIS or digital map equivalent
of matching paper maps along their edges. Features that continue over the edge
must be "zipped" together, and the edge dissolved. To edge match,
maps must be on the same projection, datum, ellipsoid, and scale, and show features
captured at the same equivalent scale. See also edge matching.
Motif: A graphical user interface standard
common on Unix workstations.
multitask: The ability of a computer's
operating system or a GIS to handle more than one process at once; for example,
editing and running a command sequence while extracting data from the database
and displaying a map.
node snap: Instructing the GIS software
to make multiple nodes or points in a single node so that the features connected
to the nodes match precisely, say, at a boundary.
on-line manual: A digital version of
a computer application manual available for searching and examination as required.
patch: A fix to a program or data set
involving a sequence of data that are to be overwritten onto an older version.
proprietary format: A data format whose
specification is a copyrighted property rather than public knowledge.
raster: A data structure for maps based
on grid cells.
relational DBMS: A database management
system based on the relational data model.
renumbering: Use of the DBMS to change
the ordering or ranges of attributes. Also, especially in raster GISs, to change
the numbers within grid cells into categories.
rubber sheeting: A statistical distortion
of two map layers so that spatial coregistration is accomplished, usually at
a set of common points.
sift: To eliminate features that are
smaller than a minimum feature size.
spatial data transfer standard (SDTS): The
formal standard specifying the organization and mechanism for the transfer of
GIS data between dissimilar computer systems. Adopted as FIPS 173 in 1992, SDTS
specifies terminology, feature types, and accuracy specifications as well as
a formal file transfer method for any generic geographic data. Subsets for the
standard for specific types of data, vector, and raster, for example, are called
spreadsheet: A computer program that
allows the user to enter numbers and text into a table with rows and columns,
and then maintain and manipulate those numbers using the table structure.
SURFACE II: An early computer mapping
package from the Kansas Geological Survey.
SYMAP: An early multipurpose computer
topologically clean: The status of a
digital vector map when all arcs that should be connected are connected at nodes
with identical coordinates and the polygons formed by connected arcs have no
duplicate, disconnected, or missing arcs.
Unix: A computer operating system that
has been made workable on virtually every possible computer and has become the
operating system of choice for workstations and science and engineering applications.
upward compatibility: The ability of
software to move on to a new version with complete support for the data, scripts,
functions and so on, of earlier versions.
user interface: The physical means of
communication between a person and a software program or operating system. At
its most basic, this is the exchange of typed statements in English or a program-like
set of commands.
vector: A map data structure using the
point or node and the connecting segment as the basic building block for representing
version: An update of software. Complete
rewrites are usually assigned entirely new version numbers (for example, Version 3),
while fixes and minor improvements are given decimal increments (e.g. Version
VisiCalc: A spreadsheet package for first-generation
microcomputers. Supported data tables in flat files.
warping: See rubber sheeting.
WIMP: A GUI term reflecting the primary
user interface tools available: windows, icons, menus, and pointers.
X-Windows: A public-domain GUI built
on the Unix operating system and computer graphics capabilities, written and
supported by the Massachusetts Institute of Technology and the basis of most
workstation shareware on the Internet.
zip: See mosaic.