


absolute georeference

The referencing in space of the location
of a point using a predefined coordinate system such as a national
grid or latitude/longitude.2

accuracy

Conforming to a recognizable standard.
If applied to paper maps or map databases, degree of conformity
with a standard or acceptable value.1
The statistical meaning of accuracy is the degree with which an
estimated mean differs from the true mean.
2

algorithm

A step by step procedure for solving
a mathematical problem.^{1}^{}

AML

Arc Macro Language

arc

A line connecting a sequence of coordinate
points. 2

aspect

A position facing a particular direction.
Usually referred to in compass directions such as degrees.1

ASCII

The American Standard
Code for Information Interchange. A standard that maps commonly
used characters such as the alphabet onto one byte long sequences
of bits. 
attribute

Nongeographic
information associated with a point, line or area in a GIS.2
An attribute is a characteristic of a feature that contains a
measurement or value for the feature. Attributes can be labels,
categories, or numbers. Attributes can be dates, standardized
values, or field or other measurements. Item for which data are
collected and organized. A column in a table or data file.

AUSLIG

Australian Surveying and Land Information
Group

AVHRR

Advanced Very High Resolution Radiometer
AVHRR The Airborne Very High Resolution Radiometer, an instrument
on the NOAA orbiting polar satellites, that returns 1 and 4 km
resolution data about the earth in 4 wavelengths. Used extensively
for large area land cover and vegetation mapping, and weather
prediction.

AVIRIS

Advanced Visible and Infrared Imaging
Spectrometer

b


boolean algebra

Boolean Algebra is useful for performing
operations on the attributes (which may be positional or descriptive)
attached to geographic entities in a GIS. Boolean Logic is especially
useful in computing (or modelling) new attributes in topological
overlay processing for both vector and raster based systems, as
they can be applied to all data types, be they Boolean, Ratio,
Interval, Ordinal, or Nominal. Boolean algebra uses the logical
operators AND, OR, NOT to determine whether a particular condition
is true or false.Each attribute can be thought of as defining
a set. Consider two sets (set A and set B). The AND operator ()
is the intersection of two sets  for example those entities that
belong to both set A and set B ( A
B). The OR operator (
) is the union of two sets  for example those entities that belong
to either set A or to set B ( A
B). The NOT operator (
) is the difference operator identifying those entities that belong
to A but not B ( A
B) These simple relations can be visualised through the use of
Venn diagrams.
For a GIS related example of the
use of these boolean logical operations, go to Boolean
Logic  Simple Interactive Example

buffer

A zone of
a given distance around a physical entity, such as a point, line
or polygon.1Buffering can also be defined as the
vector equivalent to distance analysis in raster Geographical
Information Systems. Buffering involves the creation of a zone
of a specified width around a point, line or area. The resulting
buffer is a new polygon, which can be used to determine which
entities occur within or outside the defined area.

c


cadastral
map

A map showing the precise boundaries
and size of land parcels.

cadastre

A record of interests in land, including
both the nature and extent of interests. Usually this means maps
and other descriptions of land parcels as well as the identification
of who owns certain legal rights to the land. Cadastral information
often includes other descriptive information about land parcels.1

cartesian
coordinate system

A system or two or three mutually
perpendicular axes along which any point can be precisely located
with reference to any other point, often referred to as x, y and
z coordinates. Relative measure of distance, area and direction
are constant throughout the system.1

cartographic modelling

Cartographic modelling is a general, but
welldefined methodology that is used to address diverse applications
of GIS in a clear manner. It is a technique used for both vector
and raster based GIS, and as the term suggests, cartographic modelling
involves models (ie. of geospatial information) represented in
cartographic form (ie. as Maps). Cartographic modelling is used
to simultaneously analyse both the spatial and thematic characteristics
of geospatial information. The thematic component of geospatial
information is analysed via statistical operations on the data
(for example, taking the Average and Standard Deviation of the
data), where the spatial characteristics of geospatial information
are described through spatial analysis techniques (which are based
on coordinate data). (see the Vector
Overlay module)

cell

The basic
element of spatial information in a raster data set. Cells are
always square. A group of cells forms a grid.1
(see pixel)

classification

The process of assigning items
to a group or set according to their attributes.^{
2}^{}

clump

To spatially aggregate.
To join together features with similar characteristics into a single
feature. 
COGO

coordinate geometry

composite
map

A single map created by joining
together two or more maps that have been digitised seperately.^{
2}^{}

connectivity

The topological property
of sharing a common link, such as a line connecting two points in
a network. 
contour interval

The vertical difference
in measurement units such as meters or feet, between successive
contour lines on a contour map. 
contour

A
line connecting points of equal value (e.g. elevation), often
in reference to a horizontal datum such as mean sea level.1

coordinate

The
position of a point n space with respect to a Cartesian coordinate
system (x, y and/or z values). In a GIS, a coordinate often represents
locations on the earth’s surface relative to other locations.1

coordinate
system

A
systems used to measure horizontal and vertical distances on a
plan metric map. In a GIS, it is the system whose units and characteristics
are defined by a map projection. A common coordinate systems is
used to spatially register geographic data for the same area.1

d


DBMS

database management system

DEM

Digital elevation model. A quantitative model of a topographic surface
in digital form. Also known as a ’digital terrain model’ (DTM).
The resolution, or the distance between adjacent grid points,
is a critical parameter.

digitise

A means of converting or encoding
map data that are represented in analog form into digital information
of x and y coordinates.^{1}^{}

digitiser

A device used to capture planar
coordinate data, usually as x and y coordinates from existing
analog maps for digital use.^{1}

DLG

digital line graph

double
precision

Refers to a level of coordinate
accuracy based on the possible number of significant digits that
can be stored for each coordinate. Whereas single precision coverages
can store up to 7 significant digits for each coordinate and therefore
retain a precision of +/ 5 meters in an extent of 1,000,000 meters,
double precision coverages can store up to 15 significant digits
per coordinate, and therefore retain the accuracy of much less
than 1 meter at a global extent.^{1}^{}

DPI

dots per inch, a measurement
if the density of dots used to print or scan and area with larger
values representing more detail and a finer resolution.^{
2}^{}

DTM

digital terrain model, see DEM

DXF

digital file exchange
format, a vector mode industry standard format for graphic file
exchange. 
e


eastings

The xcoordinates in a plane
coordinate system.^{1}^{}

edge matching

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. 
end node

The last point in
an arc that connects to another arc. 
f


g


GCP

ground control point

generalize

To (1) reduce the number of
points, or vertices used to represent a line; or (2) increase
the cell size and resample data in a raster format.1The
process of moving from one map scale to a smaller (less detailed)
scale and changing the form of features by simplification, etc.

geocode

A location in geographic
space converted into computer readable form. This usually means
making a digital record of the point's coordinates. 
geocoding

The activity of defining the
position of geographical objects relative to a standard reference
grid.
2
The conversion of analog maps into computer readable form. The
two usual methods of geocoding are scanning and digitizing.

Geodetical surveying

The determination of the position
of points on the earth’s surface accounting for its curvature,
rotation and gravitational field. 2

geographical
data

Data that record the location
and a value characterizing the phenomenon.2

geographic
information system

An organized collection of computer
hardware, software, geographic data and personnel designed to
efficiently capture, store, update, manipulate, analyse, and display
forms of geographically referenced information.^{1}^{}

GIF

An industry standard
raster graphic or image format. 
GPS

global positioning system, a
set of satellites in geostationary earth orbits used to help determine
geographic location anywhere on earth by means of portable electronic
receivers.^{
2}

graticule

A grid of parallels and meridians
on a map.^{1}^{}

grid

(1) a set of regularly spaced
sample points; (2) in cartography, an exact set of reference lines
over the earths surface.^{
2}

h


i


interpolation

The estimation of values of
an attribute at unsampled points from measurements made at surrounding
sites.^{
2}

interval data

Measurements that represent quantities in
terms of equal intervals or degrees of difference, but whose zero
point (or point of beginning) is arbitrarily established. Used
to quantify differences but not proportions and characterise relative
positions in space, time or magnitude. Examples include latitudes,
longitudes, compass directions, times of day and normalised scores.Interval
input map data can be used for the following statistical operations:
Sum, Average, Maximum, Minimum, Median, Majority, Minority, Diversity
(Variety) and Range. (see the Neighbourhood
Operations module)

j


JERS

Japanese Earth Resources Satellite

k


l


LANDSAT

Land resource assessment satellite
system, a series of earth resource scanning satellites launched
by the USA.^{
2}^{}

latitude

A method of measuring the earth
representing angles of a line extending from the center of the
earth to the earth’s surface. Lines of latitude run from east
to west and measure the number of degrees north or south of the
Equator (which represents 0 degrees).
Values range from the North Pole, at positive 90 degrees, to the
South Pole which is located at negative 90 degrees. Lines of latitude are often called ‘parallels’.^{1}^{}
Each degree can be further subdivided into 60 minutes, each composed
of 60 seconds.

layer

A set of digital
map features collectively (points, lines and areas) with a common
theme in coregistration with other layers. 
line

A set of ordered coordinates that
represent the shape of a geographic entity too narrow to be displayed
as an area (e.g. streams, contours).^{1}^{}

line
simplification
algorithms

Line simplification
algorithms have been developed over the years for the purpose of
'weeding out' redundant or unnecessary coordinate information from
line features, whilst retaining the perceptual characteristics of
the line. They generally work via the application of some geometric
criterion to a line's coordinate pairs (such as distance between
points or displacement from a centreline). (for more on line simplification
go to the Line Generalisation
module) 
longitude

A method of measuring the earth representing
angles of a line extending from the center of the earth to the
earth’s surface. A line extending from the north to the south
pole through the Greenwich, England, represents 0 degrees. Each
line of longitude runs north and south and measures the number
of degrees east or west of the Prime Meridian. Values range from
positive 180 to negative 180 degrees. Lines of longitude are often
called ‘meridians’. 1

lookup
table

An array of data values that
can be quickly accessed by a computer program to convert data
from one form to another.
2

m


map projection

A mathematical
model for converting locations on the earth’s surface from spherical
to planar coordinates, allowing flat maps to depict threedimensional
features. Some map projections preserve the integrity of shape,
others preserve accuracy of area, distance or direction.^{1}^{}^{
}All
map projections distort shape, area, distance or direction to
some extent.

map units

The coordinate units in which the
geographical data are stored, such as meters, or degrees, minutes
and seconds.1

meridian

A line running vertically from
the north pole to the south pole along which all locations have
the same longitude. The prime meridian (0 degrees) runs through Greenwich, England. Moving left
or right of the prime meridian, measures of longitude are negative
to the west and positive to the east, up to 180 degreees
(halfway around the globe).1

mosaicing

The GIS or digital
map equivalent of matching multiple paper maps along their edges.
Features that continue over the edge must be matched, and the edge
dissolved. A new geographic extent for the map usually has to be
cut or clipped out of the mosaic. To mosaic, maps must be on the
same projection, datum, ellipsoid, and scale, and show features
captured at the same scale. 
MSS

Multispectral scanner

n


NDVI

Normalized difference vegetation index

node

(1) the beginning or end of
a line; (2) the location where lines connect.^{1}^{}

nominal data

Values that represent qualities
rather than quantities and do so without any reference to a linear
scale (ie. 'measurement' in terms of names or designations of
discrete units or categories). Examples include telephone numbers,
post codes, or soil types.Nominal input map data can be used for
the following statistical operations: Majority, Minority, and
Diversity (Variety). (see the Neighbourhood
Operations module)

northings

The
ycoordinates in a planecoordinate system.^{1}^{}

o


ordinal data

Measurements
that quantify differences by order (ie. in terms of values such
as 'more' or 'less', 'larger' or 'smaller'), not magnitude  that
is, the size of the intervals is not specified. Often used where
quantitative differences are apparent but hard to measure (ie. when
values represent a ranked order). Examples include the distinction
between poor, moderate, and good quality agricultural land (gives
no indication of exactly how much better/worse each is than the
others). Ordinal input map data can be used for the following statistical
operations: Maximum, Minimum, Median, Majority, Minority, Diversity
(Variety) and Range. (see the Neighbourhood
Operations module) 
overlay

The process of stacking digital
representations of various spatial data on top of each other so
that each position in the area covered can be analysed in terms
of these data.^{
2}^{}

overshoot

That portion of a line digitized
past its intersection with another line.^{
}^{1}

p


photogrammetry

A series of techniques foe measuring
position and altitude from aerial photographs or images using
a stereoscope.^{
2}

pixel

One picture element of a uniform
raster or grid line. Often used synonymously with cell.^{
}^{1}

point

A single x, y coordinate that
represents a geographical feature too small to be displayed as
a line or area, e.g. a mountain peak.^{1}^{}

polygon

A vector representation of an
enclosed region, described by a sequential list of vertices or
mathematical functions.^{1}

precision

If applied to paper maps or
map databases, it means the accuracy of definition; (2) if applied
to data collection devices such as digitisers, it is the exactness
of the determined value; (3) the number of significant digits
used to store numbers.^{1}^{}^{
}Note:
precision is not the same as accuracy  a large number of significant
digits doesn't necessarily indicate that the measurement is accurate.

puck

A handheld device for entering
data from a digitiser which usually has a window with accurately
engraved crosshairs, and several buttons for entering associated
data.^{
2}^{}

q


r


ratio data

Measurements that represent quantities
in terms of equal intervals and an absolute zero point of origin.
Expressed using numbers that can be transformed or combined with
any mathematical function to generate meaningful results. Examples
include measurements of characteristics such as age, frequency,
physical distances and monetary value. Ratio input map data can
be used for the following statistical operations: Sum, Average,
Maximum, Minimum, Median, Majority, Minority, Diversity (Variety)
and Range. (see the Neighbourhood
Operations module)

raster

A regular grid of cells covering
an area.^{
2}^{}

raster data

Data where values stored for
maps and images are organized sequentially by rows and columns.
Each cell must be rectangular.^{1}^{}

rasterisation

The process of converting an
image of lines and polygons from vector representation to a gridded
representation.^{ 2}^{}

rectify

The process by which and image
or grid is converted form image coordinated to realworld coordinates.
Rectification typically involves rotation and scaling of grid
cells and thus requires resampling of values.^{1}^{}

relational database
management system (RDBMS)

A database management system
with the ability to access data organized in tabular files that
may be related together by a common field (item). An RDBMS has
the capability to recombine the data files from different files,
providing powerful tools for data usage.^{1}^{}

resampling

A technique for transforming
a raster image from one particular scale and projection to another.^{
2}^{}

resolution

(1)
The size of the smallest feature that can be represented in a
surface. (2)The accuracy at which the location and shape of map
features can be depicted for a given map scale. In a large scale
map (e.g. a map scale of 1:1) there is less reduction of features
than those shown on a small scale map (e.g. 1:1,000,000). On a
larger scale map feature resolution more closely resembles realworld
features. As map scale decreases, resolution also diminishes as
feature boundaries must be smoothed, simplified or not shown at
all.1

Root Mean Square
Error (RMS)

The Root Mean Square (RMS) error represents
the difference between original control points and new control
point locations calculated by the transformation process (e.g.
during digitising). The transformation scale indicates how much
the map being digitized will be scaled to match the realworld
coordinates.
Where:
x is the error in one dimension of a point
n is the number of points in the sample
The statistic is calculated for each
dimension (Eastings and Northings).
The vector error is computed by combining these results:
Where:
E is the error in Eastings of a point
N is the error in Northings of a point
n is the number of points in the sample 5

s


scale

The relationship existence between
distance on a map and the corresponding distance on the earth.
It is usually expressed in the following form 1:10,000, meaning
that 1 unit of measurement on the map represents 10,000 of the
same units on the earth’s surface.1
A ‘ large’ scale map is one in which a given part of the Earth
is represented by a large area on the map. Large scale maps generally
show more detail than small scale maps because at a large scale
there is more space on the map in which to show features. Large
scale maps are typically used to show site plans, local areas,
neighborhoods, towns etc. 1:2,500 is an example of a large scale.
A ‘small’ scale map is one in which a given part of the Earth
is represented by a small area on the map. Small scale maps generally
show less detail than large scale maps, but cover large parts
of the Earth. Maps with regional, national, and international
extents typically have small scales, such as 1:1,000,000. Large
scale maps typically show more detail than small scale maps, whereas
on smaller scale maps there is simply not enough room to show
all the available detail, so features such as streams and roads
often have to be represented as single lines, and area features
like cities, have to be shown as points. This is called generalization.4

scanning

A process by which information
originally in hard copy format can be rapidly converted to digital
raster form.^{1}^{}

single
precision

A lower level of coordinate
accuracy based on the possible number of significant digits which
can be stored for each coordinate. Single precision numbers can
store up to 7 significant digits for each coordinate and therefore
retain a precision of +/ 5 meters in an extent of 1,000,000 meters,
double precision coverages can store up to 15 significant digits
per coordinate (typically 13 to 14 significant digits) and therefore
retain the accuracy of much less than 1 meter at a global extent.^{1}^{}

sliver

A narrow gap between two lines
created erroneously by digitising or by the vectorisation software
of a scanner.^{
2}^{}

smoothing

A process to generalize data and remove
smaller, erratic variations.

SPOT

Satellite Pour l’Observation de la
Terra

t


tessellation

The process of dividing an area
into smaller, contiguous tiles with no gaps between them.2

TIGER

Topologically integrated geographic
encoding and referencing

TM

Thematic Mapper

topology

A term used to refer to the continuity
of space and spatial properties, such as connectivity, that are
unchanged after distortion. In GIS, this terms refers to the way
in which geographical elements are linked together.2
For example the topology of a line
includes all of its to and from nodes, and its left and right
polygons. Topology is useful in GIS because some spatial modeling
operations do not require coordinates, only topological information.

transformation

The process of converting data
from one coordinate system to another through translation, projection,
rotation and scaling. 1,
2

traingulated irregular
network (TIN)

A representation of a surface derived
from irregularly spaced sample points and breakline features.
The TIN data set includes topological relationships between points
and their proximal triangles. Each sample point has an x, y coordinate
and a surface or zvalue. These points are connected by edges
to form a set of nonoverlapping triangles that can be used to
represent a surface.1
The Triangulated
Irregular Network model is an alternative to the regular raster
of a DEM, and has been adopted in numerous GISs and automated
mapping and contouring packages.

topological
map
overlay

Topological map overlay
creates new features and attribute relations by overlaying the features
from two input map layers. Features from each input layer are combined
to create new output features. Attributes of each input feature
are combined from the two input layers to describe each new output
feature, thus creating new attribute relationships. Often, the manipulation
of multiple data layers is required to achieve the objective of
the overlay operation. This is done in a stepwise fashion  two
input layers are combined to form an intermediate layer, this intermediate
layer is then combined with a third layer to form another intermediate
layer, and so forth until the desired resultant map layer is achieved.
(see the Vector Overlay module) 
u


undershoot

A digitised line that does not quite
reach a line that it should intersect.1

Universal Transverse
Mercator (UTM)

A widely used planar coordinate system,
extending from 84 north to 80 south latitude and based on a specialised
application of the Transverse Mercator projection. The extent
of the coordinate system is broken into 60, 6 degrees (longitude)
zones. Within each zone, coordinated are usually expressed as
meters north or south of the equator and east from a reference
axis. For locations in the Northern Hemisphere, the origin is
assigned a false easting of 500,000 and a false northing of 0.
For locations in the Southern Hemisphere, the origin is assigned
a false easting of 500,000 and a false northing of 10,000,000.1

v


vector

The representation of spatial data
by points, lines and polygons.2

vector
data

A coordinatebased data structure
commonly used to represent map features. Each liner feature is
represented as a list of ordered x, y coordinated. Attributes
are associated with the feature (as opposed to a raster data structure,
which associates attributes with a grid cell). Traditional vector
data structures include arcnode models vertex one point along
a line.1

vectorisation

The conversion of point, line and
area data from a grid to a vector representation.2

viewshed

Those parts of a landscape that can
be seen from a particular point.2

w


x


y


z


zvalue

The elevation value of a surface at
a particular x, y location. Also known as the spot value or spot
elevation.1



1 

2 

3 

4


5 

