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indicator in the multi-level biophysical land classification system, all 
"first order" topographic forms may be expressed as a general relief pattern , 
in broad, reconnaissance surveys at the land region and land district levels, 
while the "second order" forms may be expressed as local relief features, 
applicable in medium-scale mapping at the land system and land type levels. 
The microrelief features are important photo-interpretation elements in a 
detailed land classification and large-scale mapping. 
General Relief Pattern 
The general relief pattern of an extensive land area may be best 
depicted on small-scale photographs or air-photo mosaics. A stereoscopic 
analysis of such features as hills, ridges or depressions, their relative 
size, shape and orientation allows a rapid stratification of the area under 
observation into landscape units that are dominated by a specific kind of 
relief. On the basis of a relative proportion of hilly, flat or depressional 
topography the landscapes may be simply grouped into relief classes for 
example, low , moderate or high , where each class expresses in a quantitative 
form a range of vertical differences within a square mile or square kilometer 
area. From the systematic analysis of these general relief classes the 
landscape units may be simply described as landscapes of low relief or plains , 
landscapes of moderate relief or hills , and landscapes of high relief or 
mountains. 
The stereogram in Figure 1 prepared from small-scale (1:80,000) 
aerial photographs illustrates such stratification of an extensive land area 
into broad physiographic units (plains, hills and mountains), delineated from 
the dominant relief classes as landscapes P, H and M. 
A plain landscape (Unit P in Fig. 1) is characterized by a high 
proportion of relatively level and gently sloping areas of low relief, where 
the height differences between the low and high points are less than 150 m. 
By the shape and general character of their upland and lowland 
components the plains may also occur as elongated low relief landscapes or 
valleys , as curvilinear landscapes consisting of contiguous lowlands and 
sloping plains, or basins , and as elevated tablelands, usually bordered by an 
escarpment on at least one side, or plateaus . Considering the relative 
topographic differences, or available relief, these landscapes may be divided 
into four relief classes: relatively flat (available relief less than 15 m), 
undulating (available relief 15 to 50 m), rolling (available relief 50-100 m), 
and roughly dissected (available relief 100 to 150 m). 
A hilly landscape as illustrated in Figure 1 (Unit H), consists of a 
succession of hills, ridges and narrow valleys. The general relief is 
moderate to high, with the height differences ranging from 150 to 700 m. The 
proportion of level terrain is usually quite small. 
A mountainous landscape (Unit M in Fig. 1) is dominated by extensive 
ridges, sharp peaks and narrow valleys with steep, long slopes. The relief is