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and absolute orientation of the stereo models. Plotting instru- 
ments are checked periodically by grid measurements at three 
Z-levels according to the method developed by P. Kaasila. The 
standard error of unit weight in the image scale has been 4-7 pm 
for instruments like Wild A7, A8 and the Stereometrograph from 
Zeiss Jena and 6-9 pm for the Stereoplagigraph C8 from Zeiss 
Oberkochen. 
Aerial Triangulation 
  
Aerial triangulation and block adjustment have been applied to a 
larger extent than earlier. This is mainly due to mapping at the 
scale of 1:400 but also due to the production of the orthophoto- 
maps for the economic map of Sweden. With respect to the basic 
maps in the scales 1:1000 and 1:2000 aerial triangulation is not 
allowed at present. Specifications for large scale mapping are 
based on regulations worked out by the Land Survey Board. These 
regulations are revised from time to time in order to follow the 
technical development. The trend is to allow determination of 
co-ordinates by photogrammetric methods for boundary points as 
well as for other points usually determined by field methods. 
Measurements for aerial triangulation are mainly made in analog 
instruments. One stereo comparator is in use for production pur- 
poses. 
Photogrammetric block adjustment in Sweden has been made accord- 
ing to the independent model method for more than ten years. 
New programs have been developed during the last four years. 
There is, for example, a block adjustment system available 
which also gives orientation data for the separate stereo models 
thus facilitating the subsequent mapping. 
Investigations concerning the accuracy of practical block trian- 
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