carried out by the Survey Dept. of the Ministry of Public Works. Before the 
war special photographs on a larger scale were also taken in connection with 
re-allotment in order to obtain maps which could also be used as a basis for 
the final maps. It was only because of the impossibility of taking new photo- 
graphs during the war that we tried to use the photographs of the Topo- 
graphical Service on a scale of 1: 20,000. As no diapositives were made of 
these photographs immediately after they had been taken, irregular shrinkage 
occurred, owing to the long storage of these films. It is therefore obvious that 
with 8 times enlargement a 1 : 2,500 map only has a limited precision. For the 
first map on which the Re-allotment Service determines the surface of each 
parcel and makes a project of new roads and of a drainage system, this is, 
however, sufficient. The definitive cadastral maps of the final situation are in 
such cases made afterwards by normal ground survey. 
A check has been made on several of these 1:2,500 maps made from 
1:20,000 photographs by comparing the position of points of intersection of 
checking lines both in the field and on the map. The mean errors in the situa- 
tion of intersection points on these lines vary between 0.2 and 0.7 metre. 
In the past two years a few new experiments ‘have been made. One of 
them is the re-allotment of “De Kolken” (Friesland). There special photo- 
graphs on a scale of 1:7,500 have been taken. For comparison purposes a 
part of this area has also been plotted from existing 1 : 20,000 photographs 
as well as from terrestrial surveys. Furthermore, the same experimental area 
has been plotted from the 1 : 7,500 photographs not only in stereoscopic plot- 
ting machines, but also from single photographs after rectifying without the 
use of any stereoscope. So far the results of this comparison are not available. 
It is feared, however, that they will be adversely influenced by irregular 
shrinkage of the film, caused either by the film itself or by the combination of 
film and camera. | E e 
A second experiment is the re-allotment of Beltrum. While photogram- 
metry is normally applied to open polder areas, Beltrum is a district with many 
hedges along the borders of the parcel. The method applied there is to enlarge 
photographs up to scale 1 : 2,500, using four control points. This is a kind of 
approximate rectifying. These enlarged photographs, which greatly accelerate 
this procedure, are used for the evaluation of the parcels. During the com- 
parison of these photographs with the field, considerable differences between 
the field and the cadastral map have been discovered and plotted from the 
photographs. The proposal for the further procedure is that the new roads and 
drainage system will be marked out in the field and measured and plotted in 
the new definitive maps. The details between this framework of roads and 
ditches may be copied by tracing from the enlarged 1 : 2,500 photographs. 
Thus maps are obtained with a precision sufficient for making the project and 
computation of the new allotments. Then the question as to what additional 
  
    
  
  
  
  
  
  
  
  
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
    
to a 
more 
plots 
part 
this 
grou 
tryir 
cisio 
157 
cade 
Oth 
of 1 
cree 
Wo 
with 
mea 
sinc 
scal 
pict 
pro, 
the 
as r 
by 
hav 
phc 
gro 
cad 
in | 
thu 
ma)