- 1410 - 
This combined approach reflects the complementary interactions which 
naturally prevail between both systems. In other words, land systems (and 
their constituent facets) constitute a most meaningful reference to a large 
number of land characteristics required for the qualitative evaluation 
assessment envisaged. 
The terrain parameters and methodology retained for the compilation of a 
reconnaissance land system map of Sierra Leone are described in detail by 
Bleeker and Birchall (1978) (see Table C). 
Bach land system is defined by a series of criteria relating to the 
following: 
— Physiography 
— Geology 
- Geomorphology 
Relief categories 
Altitude ranges 
Characteristics slopes 
- Hydrology 
- Hydrographic grain 
Drainage density 
Drainage pattern 
- Vegetation and land-use 
Table C is an example of the descriptive legend developed for use with the 
land system maps of Sierra Leone. 
For this survey black-and-white HF aerial photographs at scale 1:120,000 
(super-wide-angle) were interpreted stereoscopically and supported by 
numerous field checks and laboratory analysis of field samples - more than 
900 sites. 
Due to the frequent occurrence of haze, many of the images on the panchromatic 
photographs are somewhat "blurred", Probably IR black-and-white emulsions 
instead of panchromatic would overcome the problem of IR surveys to be carried 
out in similar or comparable climatic environments. Unfortunately, the only 
set of original colour IR transparencies was being interpreted for vegetation 
and land-use studies and the products listed in Table B were not available 
at the time. 
A later inspection of the CIR transparencies and products indicated that with 
any of these, the identification and delineation of land systems and more in 
particular the recognition of their constituent facets would have been easier, 
To palliate the problem of using the panchromatic black-and-white photographs, 
reference was systematically made to existing old photographs at scale 1:40,000, 
Their disadvantage was partly counter-balanced by the broad synoptic view 
given by the very small scale black-and-white of the high altitude panchromatic 
photographs - an important asset when studying large physiographic units such 
as land systems, 
(b) Vegetation and Land-Use Maps 
Information on the types, percentages and geographic distribution of vegetation 
and land-use patters is important for land evaluation and agricultural planning 
purposes, Indeed, it is not necessarily sufficient to know the respective 
potential as a given tract of land for specific land utilization types; but it 
    
  
   
  
   
   
   
   
   
    
    
   
   
  
   
   
   
  
   
  
   
   
   
  
  
   
  
  
  
    
  
  
   
  
  
   
  
    
  
  
  
  
  
  
  
   
  
   
    
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