d units.
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sts most
s in each
laps were
e method
ate paper
1 probab-
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dit, 1970;
e exposed
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roperties.
ither of a
the prob-
produced
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es tor the
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p percen-
-soil map
its is the
drainage,
:terfluv ial
tably the
" €" Apart from the Keana and Makurdi siopes, whose losses to tne pixel maps have been exp-
lained, the other losers are the physiographic-soil units whose pixel population have been masked
by those of the surrounding units because of their narrow shapes or small extent. These are the
depressional units — the proximal depressions and the upland valley bottom units (++).
‘ +‘ The third type of deviation is one which has been caused by other factors The sand bars
are lower in spectral maps because (1) the river Benue was drier when the aerial photographs
were shot (February, 1978) than when the LANDSAT overpass was recorded (January, 1976)
and (2) the very shallow water which were classified as sand bars by api were seen as water by the
computer and so were classified as water which by the same margin is larger than on the physio-
graphic soil map. The settlements are lower on the pixel maps because the computer discrimina-
tes better than human eyes in reflectance perception. Where api grouped structures and surroun-
ding land areas as one unit of settlement, the computer picks out only the reflectance of struc-
tures and land cover removal.
Table 1: Relative percentages of the terrain units in Physiographic-soil map and pixel maps
Physiographic-soil map
Physiographic-soil unit No of ha % MAX LIK MINI-DIST
% %
Proximal Ridge 2663 3.95 4.11 7.49 —
Proximal Depression 1441 2.14 0.65 0.78 ++
Distal Ridge complex 2794 4.15 5.04 6.79
Distal Depression complex 1065 1.58 2.78 3.26
Western Sand Island Depression 205 0.31 0.26 0.48
Western Sand Island Ridge 408 0.61 2.54 3.21 —
Western Sand Island levee 575 0.85 7.24 5.98 —
Sand Bar 3000 4.45 1.68 1.89
Awgu Fringing Forests
(Valley bottom) 867 1.29 5.68 8.20 —
Awgu Floodplain 319 0.47 10.89 11.36 —
Nearly level Makurdi slopes 1119 1.66 6.42 2.82
Upland valley bottom soils
(Keana & Makurdi) 5629 8.35 3.73 2.14 ++
Open water surface 2865 4.25 4.72 4.62
Settlements 4548 6.75 1.87 161 t
Undulating Makurdi slopes 18567 27.55 6.19 6.66 *
Keana slopes 14661 21.76 5.01 4.93 +
Awgu slopes 6166 9.15 11.42 9.94
Levees 488 0.75 4.47 3.49 —
Annually flooded sand
island-eastern) — = 4.33 4.33
Burnt areas -— ES 10.97 10.97
TOTAL 100.02 100.01 100.95
CONCLUSIONS
The conclusions from these investigations may be summarised as follows:
1. It is unwise to do any soil or resource survey in any country without taking advantage of the
huge benefits derivable from the applications of remotely-sensed data. The computer is very cost-
effective in reconnaissance soil and resource surveys, producing results very cheaply and rapidly.
86
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