(406) 
of terrain from urban and cultivated areas to the mountainous areas of Alaska 
with contour intervals of 20 to 100 feet. 
Recently rigorous accuracy tests were made on an area that was 80% 
covered with dense deciduous trees. The aerial photography had been made 
during the winter to minimize the leaf cover. The scale of the photographs and 
map manuscript was 1:20,000 and the flying height was 14,000 feet. The 
horizontal accuracy test resulted in no change either in shape or position of 
planimetry. The vertical accuracy tests found 789% of the test points to be less 
than two feet in error and only 4% in error as much as 5 feet. 'The root-mean- 
square error or standard deviation was 2 feet, giving a permissible contour 
interval of 8 feet. The corresponding C-factor calculates to be 1750. 
STEREO-MAPS 
by 
A. Frey Samsioe, Dr. Techn. and Percy H. Tham, Dr. Techn., Stockholm. 
Since the 6th International Congress of Photogrammetry was held in the 
Hague in 1948, various types of maps, permitting a three-dimensional presen- 
tation of terrain, have been discussed. Instead of the traditional contour lines, 
with their limitations, direct reproduction of the ground has been the ultimate 
aim. 
The moulded relief maps of plastic material, particularly used in the U.S.A. 
are an interesting development. By the exaggeration of the height scale the 
model gives an impression similar to that obtained by a pair of pictures stereo- 
scopically observed. 
Whth regard to stereo maps, a new type is proposed by W. A. Brucklacber, 
described in Bildmessung und Luftbildwesen, 1/1950, Berlin. This “map”, 
however, is not a real map, but is a systematic assembling of pairs of pictures in 
such a manner that a *window-frame effect" is obtained. This "grid" aids the 
visual relief impression. The use of this method, as is mentionned by the 
proposer, depends on a very good flight performance and also on the fulfilment 
of other necessary conditions. Brucklacher goes on to say that the production 
of a true-to-nature anaglyph map would be impossible in view of the central 
projection of the image. 
In actual fact the production of such a map is possible, and the authors 
have made an anaglyph Map that is completely true to nature. It is composed 
of about 7 pictures fitted together in conformity with the “compilation” 
method used in Sweden. A check of the accuracy of the map has fully 
established that it is impossible to find the boundaries of the pictures when 
observing the map wth a mirror stereoscope. In presenting this map it needs 
only be said that the right (red) *master map" is a normal map true to scale; 
the left (blue) "parallax map" gives the necessary parallaxes. There are no other 
points to be taken into consideration other than that of increasing the overlap 
to the double, i.e. from 60% to 80%. With these pictures on file, it will always 
be possible to obtain a three-dimensional map.