It was not possible to determine what proportion 
of the total length of paths was detectable, as 
this would involve very elaborate field work. 
It is estimated that not more than 10% of all the 
paths are identifiable on the image. 
4.1.2 Settlements, compounds and buildings 
Settlements can be clearly identified and adequa- 
tely demarcated. Isolated buildings are also reco- 
gnizable, however compounds, as isolated group of 
buildings are not identifiable due to the scale of 
the image. 
4.2 Test area 2 
4.2.1 Roads 
The road network of the second area comprises mi- 
nor roads and paths. Figures 3 show the map of 
this area and a plot of the identifiable roads. 
  
Fig. 3(b): Plot of Road network and 
boundary of settlement in Area 2. 
Minor roads 
An overlay of the map with the plotted roads shows 
that only about 50% of the total length of minor 
roads is detectable in this area. 
Part of the reason for the poor result here is 
the state of the roads which is much worse than in 
the first area. Portions of the roads are over- 
grown with weeds, while parts are occluded by 
trees above. The course of the roads in such sec- 
tions are usually unrecognizable on the image. 
Also, where roads pass through or follow bound- 
aries of settlements, the course becomes undetec- 
table. 
Except for some of the old paths which now appears 
to have been "upgraded" to minor roads, no paths 
are detectable on the image of this area. 
4.2.2 Settlements, Compounds and Buildings 
Due to their high reflectance in contrast to the 
surrounding vegetation, settlements and isolated 
430 
buildings can be identified. On the other hand, 
compounds are not recognizable. 
5. OVERALL ASSESSMENT 
The image is suitable for identification of main 
roads. 
Minor roads are identifiable provided they are at 
least 5 meters wide. 
Paths are generally not detectable on the image. 
This is partly due to the fact that the width is 
too small for the spatial resolution of the sen- 
sor, and partly to the fact that some of these 
tracks often run through woods and can therefore 
not be seen from above. 
Pathways are sometimes the only communication 
links between rural communities and are therefore 
important features on topographic maps of such 
areas. Detail survey of these tracks have to be 
done by ground survey. 
Settlements can be clearly recognized on the image 
and their boundaries sufficiently demarcated. Iso- 
lated buildings can also be identified. Identifi- 
cation of compounds is however not possible. 
Change detection of settlements can be adequately. 
done out using the image. 
Apart from deficiencies in the detection of some 
map details as seen above, the use of space images 
for topographic mapping may not become popular in 
most developing countries for some time to come 
due to some operational problems peculiar to these 
countries. 
In most developing countries, ground controls for 
geometric restitution of the images would, almost 
invariably, have to be provided through ground 
survey methods since large scale maps are gene- 
rally not available. 
Provision of ground controls by the traditional 
methods of land surveying (traversing etc) for a 
full image scene may take a long time considering 
that the geodetic control nets are in most cases 
poorly densified. 
The cost of GPS positioning equipment, with which 
control points can be more easily and quickly 
established, restricts their use in most develo- 
ping countries. 
Since the available maps are usually too old to be 
used as reliable references, very extensive and 
time-consuming field verification woud be required 
to assess the amount of omission commision errors 
in the image interpretation and plotting. Ground 
verification with satellite images is a very te- 
dious task because of the small scale of the 
images. In most cases, such checks have to be sup- 
ported by the use of aerial photographs which are 
not always available. 
The instrumentation requirements for mapping from 
satellite images is likely to discourage the use 
of this method in most developing countries. The 
available analogue plotters are unsuitable because 
of the image geometry. Analytical plotters are 
beyond the reach of many survey departments be- 
cause of their costs. Even where they are avai- 
lable, maintenance poses a great problem as break- 
down is very frequent due to power fluctuations 
and bad handling. 
If the use of space images for mapping is to be 
fully operational in developing countries, there 
must be the possibility of carring out projects 
using the locally available manpower. 
Experience has shown that there is a dearth of 
qualified personnel in photogrammetry and carto- 
graphy in most of the countries, with the result 
that most of the operations involved in map pro- 
soc 
CHE VQOMXK