d) if recording of projects executed is essential, or if distinct stand 
boundaries are required for stand descriptions or check of prescribed 
measures 
e) if the personnel is on the old side 
f) if there are great differences in elevation of the ground and local 
errors in scale must be avoided. 
As a rule, aerial photos will be most suitable in other cases and parti- 
cularly 
a) if suitable aerial photos are already available 
b) if the personnel is young and experienced in photo interpretation 
c) if the mapping procedure must be quick and inexpensive 
d) if stereo studies of stands etc. can be applied to the planning of 
measures etc. and thus replace stand descriptions (including data of 
species composition) 
e) if orientation — particularly local orientation — requires to be 
facilitated. 
The photos will probably eventually supersede the drawn maps as photo 
material becomes better in respect of definition and trueness to scale. 
In Northern Sweden this transition is well under way and may be expected 
to be more or less completed in the next decade or two. In Southern Sweden 
progress in this direction is slower and the drawn map will probably main- 
tain itself in several places side by side with the air photos for some time 
yet. Possibly drawn maps or sketches will continue to be ordinary comple- 
ments to photo prints, even in Norrland, if fully adequate cartographic 
instruments come into use in this country. 
9. Contour lines have been employed to a surprisingly small extent, 
though in many districts these are available from the work of the Geo- 
graphical Survey Offices. Expense does not provide a full explanation. 
Stereo-vision together with available data for altitudes of scattered spots 
will often suffice for the planning of the hauling of the timber, particularly 
in forests where there is a good network of roads and differences in 
elevation are comparatively negligible. The contour line intervals are often 
too wide (5 or 10 m interval) and moreover the contour lines hamper the 
use of photo maps for other purposes. It is worth noting that one of the 
companies has preferred to mark the slope of the ground on its drawn 
maps by hatchings drawn in on the basis of the contour lines. 
3. Distinct marking of trails, streams etc. on the photos by drawing 
presents a problem. If complements to the photos in the form of drawn 
maps are lacking, the drawing in of some details cannot be avoided. This 
impairs photo interpretation, however, and must be restricted as far as 
possible, especially on photos of good quality. As a rule it has been found 
that the addition of drawing to photos takes up more time than was anti- 
cipated. In particular, the plotting of property boundary lines has in many 
cases led to increase in expenditure of time and money. Marking of the 
boundaries on the ground by swamping and the setting up of signals be- 
fore the photos are taken has only rarely proved entirely satisfactory, 
the failure being due to hurry and inadequate knowledge of photogram- 
metry. In many forest districts and in State forests, the property boundaries 
can for the most part be easily identified on the photos. 
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