2 
interpretatian is the planning of roads, drainages, boundary and land 
estate systems etc. 
A map compilation of planimetry by photogrammetric methods is 
based on photointerpretation. So it must be a dependence between the 
accuracy of interpretation and the accuracy of compilation. It is tried 
here among other things to find suitable variables for determining the 
accuracy of interpretation and compilation. 
1.3. In the article before us there is given an account of some inves- 
tigations of the Swedish Land Survey, concerning the mapping out of 
forested land, the site classification, the determination of stand volume, 
the technique of photointerpretation when using control from helicop 
ter and also concerning some experiences from two large reallotments 
in northern Sweden. 
2. The mapping out of forested land 
2.1. Conceptions and terms. Once the network and the aerial photo- 
graphy are completed, the next step in the preparation of map is to add 
planimetric detail such as lakes, rivers, streams, roads, buildings, boun- 
daries of landed estates, forest stand boundaries, swamps, hills, ridges 
etc. This procedure regarding forested land is here called mapping 
out. It is a selection from the infinite great number of ground details 
of the ones, necessary for the purpose of mapping. Their positions are 
determined by drawing on the photographs and later on by transfor 
ming these drawn lines in a photogrammetric plotter from central to 
orthogonal projection. It is obvious that some of the details may be 
identified rather sharply, e. g. buildings, boundaries of landed estates 
and roads, but other details more unsharply e. g. swamps and bounda- 
ries of site classes etc. A map detail, e. g. a forest stand or a swamp, ls 
an irregularly formed piece of ground, here called section, the boundary 
of which here is called section-line. 
2.2. The problem to be studied. Photointerpretation is performed in 
three steps. 
a) Cruise lines are located in the field especially over high producing 
forested areas as narrow winding zones, in which sample plots are ar 
ranged and measured in respect of forestry elements. All areas in the 
zones are also estimated visually as to soil, moisture, tree species, forest 
site etc. The informations are noted on the photographs. So a correla- 
tion is found between informations in the field and the corresponding 
informations on the photographs. 
b) Photointerpretation of all the areas in between the zones 1s per- 
formed indoors by the use of mirror stereoscope. The informations are 
also noted on the photographs. 
c) Finally a field control of some small scattered areas may be ne- 
cessary. It can advantageously be executed from helicopter.