which may involve stream gauging and other hydrological studies to determine 
seasonal capacity and fluctuations and also an assessment, often including 
photo-geological and field investigations, of potential dam sites for hydro 
electric power plants. At this stage of the pre-investment survey the surveyors 
carrying out the work may call for additional large scale photography of 
selected areas and, at these sites, more detailed topographic maps will be made 
to obtain accurate cost estimates for the engineering works which are being 
considered. But this stage will only be reached if an evaluation of the other 
factors already mentioned shows that the project is promising. 
At this time too, studies will be made of potential labour supply, which 
will include an assessment of how much skilled, semi-skilled and unskilled 
labour will be needed, and of such matters as the purity of the water, partic 
ularly where it will be used in the manufacturing process, of possibilities for 
effluent disposal - especially important in the case of chemical paper mills, 
and of other minor but none the less relative factors such as government 
inducements to the establishment of pioneer industries by giving tax reliefs 
or tariff protection and so on. 
Techniques 
I hope that I have given some of you here today food for thought about 
pre-investment surveys. The intention was to take you beyond the relatively 
narrow limits of photo interpretation of vegetation types and to bring you to 
appreciate what other aspects must also be considered when carrying out pre 
investment surveys. Now, if you will permit me, I will say a few more words 
on particular techniques and recent developments which are so relevant to 
matters discussed at this symposium. 
The first concerns aerial photography. Improved cameras, improved optics, 
improved films, and improved navigational techniques have all led to a more 
economical photographic coverage of project areas. Electronic printers have 
also been developed which result in better prints for interpretation purposes. 
Of particular interest is the recent development of super-wide angle photo 
graphy which is suited to small scale overall appraisals of large areas. This 
new development is also suited to the economical provision of ground control, 
which, in this day and age, is often provided by means of electronic distance 
measuring instruments. Already we, in F.A.O., are using electronic distance 
measuring instruments to speed up forest survey work in Mexico. And this 
development, a widely used tool of ground surveyors, will probably - with 
its refinements - become much more commonly used in certain types of 
resource appraisals. The use of airborne electronic distance measuring equip 
ment, for example the airborne profile recorder, is of special relevance when 
carrying out surveys for development in countries for which limited ground 
control exists. This technique is growing in importance and, particularly in 
the case of forest areas lying near lakes or coastlines, it provides an accurate 
basis for the compilation of suitable topographic maps with which can be 
combined forest type maps.