1. INTRODUCTION 
The science of 'remote sensing' in its broadest 
sense has been developing since the 19th 
century with the invention of photography and 
the first aerial photographs taken from captive 
balloons. Throughout the 20th century, 
technological advances in a number of areas - 
the development of colour and infra-red 
sensitive films, aircraft and satellite platforms - 
enlarged the sphere of remote sensing with the 
development of applications such as mapping, 
geological exploration and meteorology making 
use of remotely sensed images. Remote sensing 
as it is currently practised, however, began 
with two major advances in technology - the 
launch of high resolution digital imaging 
systems (starting with Landsat-1 in 1972) and 
the development of minicomputers and image- 
display terminals in the 1970s. 
With these advances, image processing systems 
rapidly evolved. By the early 1980s, a typical 
system would have functionality for image 
input, geometric correction, classification 
(supervised and unsupervised), image 
enhancement, convolution, arithmetic functions 
(eg. band rationing) and principal components 
analysis. These would be performed as batch 
or interactive operations, with special frame- 
store hardware used for image display. 
The evolution continued throughout the 1980s, 
with an increased range of processing 
functions, data from new sensors (Landsat TM, 
SPOT, radar, airborne multispectral scanners), 
faster processors, higher resolution displays 
and user-friendly menu interfaces. Interfaces to 
vector data were provided by most systems, 
although with functionality largely limited to 
the overlay of vector data on imagery. 
Geographic Information Systems (GIS), 
however, have developed from three largely 
separate origins. The Canada Geographic 
Information System (CGIS) was first proposed 
in 1963 and was designed for overlaying vector 
polygons of resource information for 
applications such as land use assessment. A 
different approach to the same problem was 
adopted by the Harvard Laboratory for 
384 
Computer Graphics SYMAP system in the late 
1960s, which performed overlay analysis with 
raster data. These systems were the precursors 
to the present-day systems designed primarily 
for data overlay. 
A second origin to GIS was the development 
of vector-based digital mapping starting in the 
late 1960s. Digital mapping systems have 
evolved to the state where many map 
production flowlines now use computer 
technology for the manipulation of data. GIS 
systems have grown from digital mapping 
systems by the addition of a relational database 
for the storage of attribute data and by the 
provision of analytical functionality. The vector 
data model that has become dominant in this 
strand of GIS development, because line maps 
were familiar to the first generation of GIS 
users, involved in applications such as property 
management and the utilities. Vector mapping 
systems allowed them to replicate, in digital 
form, their conventional methods of working. 
A third route for the development of GIS 
systems, also based on the vector data model, 
was by a similar evolution from the Computer- 
Aided Design (CAD) area. 
GIS systems from each of these three origins 
have evolved towards a common basic range of 
capabilities - input, display and manipulation 
of both vector and raster data, raster DTM 
handling, topological structuring of vector data, 
vector and/or raster polygon modelling and 
analysis, and storage of attribute data in a 
relational database management system. Most 
systems today have the ability to perform basic 
image handling tasks, such as rectification and 
display as an image backdrop. Some systems 
allow an image processing package to share the 
same screen as the GIS, giving access to both 
image processing and GIS functionality. In 
addition, modern GIS system architectures can 
handle large raster and vector datasets in a 
seamless manner, so image processing can 
escape the constraints of image scenes and map 
data can escape the fetters of sheet boundaries. 
2, €UI 
SE 
It is us 
divisio 
occurr 
e The 
fun 
a re 
date 
dra 
mox 
up’. 
con 
plot 
unc 
diff 
toge 
e Rer 
fun 
rem 
infc 
or 
pro 
labe 
'Col 
vec 
obj 
’roe 
Ren 
con 
whe 
ana 
rec 
loc: 
may 
pro 
* His 
tecl 
disc 
tect 
tect 
was 
con 
disc 
byl 
for