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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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