REPORT OF COMMISSION VII 
GVII-91 
ders melting, wavering, advancing, retreating. 
If by some cataclysm sharp lines of demarca 
tion are drawn, she straightway begins to blur 
them by creating intermediate forms, and thus 
establishes the boundary zone which character 
izes the inanimate and animate world.” 
In these broad zones of transition 
terrain characteristic of one area fre 
quently interlocks like a jigsaw puzzle with 
terrain characteristic of another. The 
interpreter who tries to analyze a photo 
near one of these boundaries is very likely 
to find in his photos an outlier or protrud 
ing tongue of another area which is much 
different from that described for this loca 
tion. As a result the inexperienced inter- 
(10). Since each major land type has its 
own associations and ground conditions, 
the key is forced to spell out the conditions 
found on each land type within the sub 
division, a situation involving voluminous 
repetition from one subdivision to another, 
or to give vague generalizations. The latter 
alternative is the natural choice. To over 
come this objection the physiographer 
can continue to subdivide his land units 
until he reaches a unit which is homo 
geneous. If he should attempt to sub 
divide the Navajo Section into homo 
geneous units, he would find he had per 
haps 10 uplifted mountain areas, on which 
the associations were essentially the same, 
/\Jluvial Ptqin 
Photo sr2\ 
tocabon\ \ 
-boundary at chorogrqpbic. See?/es 
/—boundary at topograph* Scales 
/ Erosionq! Plain 
Fig. 2.—Two boundary lines represent the same topo 
graphic change at different scales. The smooth line is an 
average location which may be inaccurate at any given 
point if examined at a topographic scale. Here a photo falls 
within an erosional plain, but the regional map tells the 
interpreter that it is on an alluvial plain. 
prefer submits a false report, and the 
experienced man discovers his mistake, but 
makes a mental reservation regarding the 
value of the key. Figure 2 illustrates the 
problem. 
2. The greatest disadvantage of physio 
graphic subdivision is the lack of homo 
geneity within any large area such as one of 
Fenneman’s subdivisions. Any subdivision 
of the earth which does not follow generic 
land form lines has many terrain conditions 
within it. Definite ground conditions and 
associations cannot be described and only 
broad generalizations can be given. Nor 
can deductive methods for making an exact 
interpretation be outlined, like those de 
scribed by the author in a previous paper 
and perhaps 100 high plateaus with similar 
associations. This would give him far too 
much repetition, and he would be forced to 
describe the typical situation. In other 
words, there is apparently no compromise 
between “too large” and “too small” 
which does not involve voluminous repeti 
tion, unless one resorts to types. 
However, there are some regions where 
topographic changes are relatively minor 
and the land surface is relatively uniform, 
as in a level desert region, where dominant 
control shifts from topography to climate 
and water supply. In such cases the use of 
physiographic subdivisions should be con 
sidered. 
(continued on page 101)