3 
Though a more detailed discussion is outside the scope of this general report, it 
seems worth while to mention that the work of Heinsdijk in the forests of Surinam 
represents an important contribution towards the general progress of photo-interpretation 
in tropical regions. Mr. Heinsdijk who now is occupied with forest inventory work in 
Brazil has there the opportunity to use aerial photographs and apply his experience gain- 
ed in Surinam. 
Another rather interesting example of the use of aerial photography in more detailed 
forest inventory work in the tropies is the work of the Forest Officer of the Colonial 
Survey, Mr. Cahusac, in a forest region in Uganda (Africa). During 6 years Mr. Cahusac 
has been in charge of the supervision of the Budongo and Siba forest region, situated on 
the plateau south-east of Lake Albert in Uganda. Although in previous years the general 
composition of these forests had intensively been studied by former forest officers (Eg- 
geling) [3], the knowledge of the distribution of the different types over the whole area 
was rather incomplete as good forest maps of this region were lacking. As these forests 
were very valuable for exploitatión purposes and some logging companies already had 
started cutting the most valuable tree species, a good map showing the distribution of 
the different forest types over the whole area was absolutely necessary to plan future 
exploitation procedures. 
This was the reason why Mr. Cahusac decided to use his European leave for a stay of 
a few months at the L T.C. in Delft. His intention was to obtain there a training in general 
interpretation techniques of aerial photographs in order to apply this knowledge to make 
a type map of the Budonga forest region. For this purpose he brought a set of photo- 
graphs of the Budonga forest region with him, made on a scale of 1 : 30.000. After a pre- 
liminary training at the LT.C. Mr. Cahusac started with his own photographs. He was 
able to identify on them the boundaries of the different forest types. These boundaries 
were marked on the photographs and afterwards transferred to the base map. The situa- 
tion of the passpoints in the base map was determined by the usual slotted templet method 
which is supposed to be accurate enough for making forest type maps. As local differen- 
ces in elevation were small in comparison with flying heights (the whole region was 
situated on a plat form at an average altitude of about 1000 m above sea level), it was 
not difficult to fit the templates together; also the plotting of the vegetation boundaries 
into the base map could be achieved by using simple plotting instruments like the Sketch- 
master or Rectoplanigraph. 
It is important to emphasize in this connection that the forester dealing with general 
forest inventory work in the tropical regions should learn not only pure interpretation 
techniques, but also have some general knowledge of how the interpretation results can 
be compiled into a map with an accuracy sufficient for this special purposes. 
As a matter of fact the interpretation of the different forest types took an important 
part of the time Mr. Cahusac spent at our institute. Although he had not the opportunity 
to check the results obtained from the photographs with the situation in the field, Mr. 
Cahusac was nevertheless able to identify the different types in the photographs and 
classify their features. This classification was based on apparent differences in tree spe- 
cies in the dominant crown canopy. This result could only be achieved through Mr. Ca- 
husac’s local experience. 
1 
This case may serve as an example of useful cooperation between training possibili- 
ties at the LT.C. and practical knowledge obtained in the field to obtain results which are 
valuable to forestry management procedures in different parts of the world. 
Besides the training of several foreign foresters in different fields of photo-inter- 
pretation the Forestry Section of this institute has during the last 4 years also been 
engaged in preparing vegetation maps of different regions in Dutch New Guinea (East- 
ern Asia). These maps are based on interpretation results obtained from prewar vertical 
photographs at a scale of abt. 1:40.000. During successive periods a total area of abt. 
10.000 sq, km was mapped at the same scale (1 : 40.000). The situation of the passpoints