Land capability analysis using computerised overlay techniques
Date
2015-01-23
Authors
Hammond, C. M.
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Abstract
A versatile computerised overlay technique to
analyse relatively constant, objectively measured, land
characteristics for their capability to sustain any defined
land use was developed. The mapped form of each land
characteristic, be it of a polygonal, network or discrete
point distribution is stored in a data base system for
subsequent retrieval and overlay by a grid of selected cell
size. The capability rating of each measured land
characteristic value is derived from a capability graph or
table which relates this value to a capability scale
according to existing information. A foreclosure of
options in land use is also performed. The influence of
each characteristic upon the overall capability for a
defined land use is included by user defined weighting
values. The overall capability of an overlaid grid cell
is the weighted mean of the individual capability values
for each land characteristic analysed. The result is
mapped by overprinting on a line printer.
Information to select the land characteristics
analysed for a land use, to develop the capability graphs
and tables, to quantitatively analyse interrelationships
between land characteristics and to define weighting values
was gathered from the literature and various people. This
information which controlled the analysis of the land for a
land use and default sets of weighting values used if the
user makes no choice, are stored in the data base system.
The capability analysis program is composed of a suite of
interactive and non-interactive FORTRAN programs.
A trial run of the procedure was compared with a
ranual land capability analysis for an agricultural land
use in Northern Lebowa, South Africa. The results
illustrated the influence on tfo overall capability of both
the weighting value and the selected overlay grid cell size.
The value of a versatile capability analysis tool which can
analyse any defined land use, using selected weighting
values and grid cell sizes, was seen. The procedure is
also not restricted by the study area size, the scale at
which the land is surveyed, the choice of land characteristics
used in the analysis, the shape of the capability graphs
and the values contained in the capability tables.