May, 1960 Commission VII 195 
K. B. Jackson of the interpretation problems involved have led to a considerable 
improvement in the specifications for photography. Distortion limits were much more 
rigidly set, the exposure interval was limited to not greater than 1/300 second and the 
actual exposure (considering both aperture and shutter) is specified as that placing 
the range of negative densities on the straight line portion of the D log E curve. In 
addition, prints are made on a paper suitable for viewing by transmitted light. 
MANITOBA DEPARTMENT OF Mines & Resources. The forestry inventory of Mani- 
toba, based on the interpretation of aerial photographs and field work, was completed 
in 1956. During the period under review 5,950 sq. miles have been re-photographed 
for the interpretation of forest data. This photography was summer panchromatic at 
1:15,840. Type boundaries are interpreted from the photographs and the remainder 
of the information required is collected in the field. Interpretation is also used, as a 
standard practice, for forest road locations and some 400 miles of main highway have 
been located also by interpretation methods. Water resources surveys showing areas 
to be flooded by new dams were made by photo-interpretation in the Duck Mountain 
and Porcupine Forest Reserves, and for the major projects on the Nelson and Saskatch- 
ewan rivers. 
SASKATCHEWAN DEPARTMENT OF NATURAL Resources. Saskatchewan completed its 
forest inventory, using photo-interpretation extensively, in March 1956. Since then 
some 1500 square miles have been re-photographed each year at 1:15,840. Panchro- 
matic photography is used during the spring and fall, and modified infrared during 
the summer months. Interpretation produces the forest classification, and volumetric 
data are obtained by field sampling. However, some volume estimates have been made 
successfully on small areas with the use of stereograms. Forest road locations, much 
of the detail for logging plans, and fire protection plans are obtained from photographic 
interpretation. The Zeiss Stereopret has proved valuable in all types of interpretation. 
AIBERTA ForksT Service. Alberta completed its forest inventory, based like those 
of the other provinces on a combination of photo-interpretation and field work, before 
1956. Since then, some 33,000 square miles have been re-photographed at the inven- 
tory scale of 1:15,840. Modified infrared has been used generally, with a 6-inch lens 
for level terrain, and a 12-inch lens for alpine and sub-alpine areas. Interpretation of 
these photographs gives the height class, density class and species group, while field 
work provides the volumetric data. 
Research is under way to work out a method of classifying forest sites by inter- 
pretation of land form. 
Interpretation is also relied on to keep the provincial maps up to date with respect 
to forest roads and trails. 
Britis COLUMBIA DEPARTMENT oF LANDs & Forests. The provincial forest inven- 
tory began in 1951 and by 1956, the start of the period of this report, 70 percent of the 
273,000 square miles of accessible forest of the province had been inventoried. 
Since 1957 photography has been taken at 1:15,840 using an F24 camera modified 
to take a 7-inch lens. This has been summer photography using panchromatic film. 
During 1957 and 1958, 28,000 square miles were photographed. In interpretation, tree 
heights are measured with a parallax bar and stand density is estimated. This is 
supplemented by field work and helicopter observations. 
Private Companies. The interpretation of aerial photographs is universal among 
pulp and paper companies for the purpose of estimating timber in conjunction with 
field measurements. The methods are parallel to those used for inventory by the 
various government organizations, and use the same scales and types of photography. 
A method of using large-scale photographs (1:1600) to sample the area covered by 
medium-scale photography (1:8000) has been developed and tested with gocd results