REPORT OF COMMISSION VII 
GVII-83 
explain each of the other sections of the 
province shown in Plates 5 through 7. An 
adaptation of the methods of Bowman and 
the Michigan Economic Land Survey is 
demonstrated by means of a key to the 
terrain types of the Colorado Plateau, 
keying out the basin type, shown in Plates 8 
through 13. This is followed by single 
oblique photos representing each of the 
other terrain types, shown in Plates 14 
through 16, so that their characteristics 
may be understood. Keys to geographic 
areas are usually part of a more extensive 
series of keys, including keys to the in 
dividual elements of terrain, with which 
the area keys are coordinated. Collectively 
this group of mutually supporting keys is 
known as a “regional key.” 
The terrain types used herein are pre 
liminary selections and revisions could be 
expected following extensive study. It 
should be kept in mind that although the 
types have been given geomorphic names 
they are not merely land form types but 
associations of many related terrain elements. 
These basic types could be further broken 
down into land-use classes if an intensive 
survey were to be made, but in any broad 
land-use survey they could form the 
foundation for understanding man’s en 
vironment. Despite the importance of the 
physical elements no attempt has been 
made to limit man’s environment to phys 
ical geography alone, and social factors are 
recognized wherever they apply. 
The Colorado Plateau is one of the 
physiographic provinces described by both 
Bowman and Fenneman, and it was 
chosen as the region for demonstration 
because the author knows many parts of it 
intimately after spending 6 years on it as a 
land manager. Much of this time was 
spent in the study of ecological relation 
ships involved in the complex range man 
agement problems of that region. Photo 
interpretation was one of the methods of 
investigation used by the author, and air 
photos were constantly carried in his 
saddle bags. This province makes a good 
example to illustrate differences in terrain 
because the environmental contrasts be 
tween its types reach great extremes. 
There are similar contrasts in other regions 
but they are muted by gradual changes in 
relief and climate, making analysis of 
associations more complicated. 
Physiographic Subdivision 
ADVANTAGES 
1. Physiographic subdivisions permit 
complete description of a region, with each 
unit receiving its appropriate share of 
attention. When information on an area is 
sought, either to plan operations within it, 
or to investigate activity in the area, it is 
merely necessary to turn to the right page 
and a description of the area is found. 
Where complete photo coverage is avail 
able experienced analysts can do the photo 
interpretation for each area in advance and 
can present a complete analysis ready 
made for the user. This can be mapped on 
mosaics so that the location of each terrain 
condition is unmistakable. This, of course, 
would be very time consuming and expen 
sive. 
2. The subdivision method highlights 
changes in conditions in various parts of a 
region. One area is either drier or wetter, 
colder or warmer than another, and these 
differences inevitably affect the environ 
ment and man’s use of terrain. Therefore, 
if climate is a controlling factor, serious 
consideration should be given to subdivi 
sion by either physiographic or climatic 
subdivisions. Regions may also show eco 
nomic changes from locality to locality. 
These changes are not necessarily coinci 
dent with physiographic subdivisions, but 
physiographic barriers and avenues of 
movement frequently contribute to eco 
nomic unity. 
3. Research for this method is simplified 
by the existence of many physiographic 
studies, which may be reorganized and 
condensed to suit the needs of a regional 
key. 
4. The physiographic type of key is 
simple and straightforward and is adopted 
to use by many levels, from students to 
advanced researchers. 
DISADVANTAGES 
1. Since physiographic subdivisions con 
tain many land forms and are vague and 
unrecognizable on air photos, the investi 
gator must depend upon a regional map 
as a key to his air photos. He is first of 
all exposed to two sources of error, map 
location and photo location errors, either 
of which can upset his estimates. 
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