INTRODUCTION 
The newly independent developing nations, as well 
as the highly industrialized states, place an ever-increasing 
demand on the presently available natural resources. The 
expanding use and fast consumption of our resources make it 
necessary to explore the unknown and inaccessible parts of the 
world in the hope of finding new areas for agriculture, hydro 
electric power sites, communication routes, forest reserves, 
oil and minerals. 
In recent years, the policy-making bodies in many 
countries have become more conscious of the fact that suitable 
maps are an essential prerequisite to effective exploration 
and orderly development planning of a region. This awareness 
was probably brought about by the spectacular achievements in 
mapping the moon, prior to sending of a manned space vehicle. 
That costly mapping exercise dramatically brought to the 
attention of the planners, as well as the ordinary tax payers, 
the need for mapping as a first step to exploration and develop- 
ment. 
A large percentage of the unexplored areas of the 
world lie in tropical and inaccessible regions with weather 
conditions unfavourable to aerial photography. The obstacles