435
Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Land use from aerial photographs: A case study
in the Nigerian Savannah
NJ.Field
Department of Surveying, Ahmadu Bello University, Zaria, Nigeria
W.G. Collins
Department of Civil Engineering & Construction, Aston University, Birmingham, UK
ABSTRACT: Using medium scale photographs it was possible to estimate the land
use in a test area of the Nigerian Savannah. A method of primary and secondary
sampling was applied covering about 17% of the area. Significant changes were
noted between 1950 and 1972 in woodland, farmland, and grass/scrub.
Correlations were noted between accessibility and changes in land use.
1. OBJECT OF THE PROJECT
1.1 The object of this project was to devise a
method for monitoring land use and land use
changes over .areas of the Nigerian savannah
region, using available aerial photography and
simple interpretation techniques. Information on
land use and land resources is not readily
available and although methods using satellite
data are very efficient they tend to be out of the
reach of the ordinary user in a developing country
because of expense and the lack of equipment for
interpretation.
1.2 There is a large amount of aerial
photography of Nigeria which has been flown at
different times and was designed for use in the
production of topographical maps. This material
is archived after use, and still contains a wealth
of information on vegetation and land use which
has not been transferred to the topographical
maps produced from it. As Philipson (1980) says,
"if the aerial photography is available, the
expense of acquiring and analysing other forms of
remote sensing may not be justifiable."
1.3 The .project makes use of some of this
material and obtains land use data from it with
simple photointerpretation equipment such as would
be available in most small survey organisations.
Because of the large volume of data and the
statistical tests which are necessary to test its
relevance a microcomputer has been used in the
processing of the information. It has been shown
by Emmott (1981) in a pioneering study that"The
Combination of conventional photointerpretation
techniques with widely available computer
facilities provides an efficient means for the
measurement, storage and representation of land use
data".
2. CHOICE OF TEST AREA
2.1 The test area is covered by the national map
series Nigeria 1:50,000 sheet 145 NW Kajuru, and
is an approximate rectangle bounded by longitudes
7°30 E 7°45 E; and latitudes 10°15'n, IOOso'N;
with an approximate area of 750 sq km. The
boundaries were slightly modified because of the
photographic coverage.
The area is situated in the southern part of
Kaduna State immediately to the S.E. of the large
industrial and administrative centre of Kaduna.
The topography consists of gently undulating
plains wide valleys (fadama) , the plains being
interrupted in the S.W. by frequent rocky hills
(inselbergs) (see figures 1 and 2) . The
vegetation and climate are typical of the savannah
with a 5-6 month growing period during the rains
from April to September (Kowal and Knabe 1972) and
it falls within the Northern Guinea savannah zone
(LRDC 1979) recognised by some writers.
Population density is nowhere very high, although
several new market villages have developed over
the last 30 years. Communications are generally
poor, but there has been a certain amount of road
improvement recently which has improved
accessibility. (see figure 3).
2.2 The test area was chosen for five reasons:
1. It is fairly representative of the savannah;
neither too far south to contain large areas of
forest or derived savannah, nor far enough north
to contain Sudan or Sahel vegetation.
2. The terrain and climate give rise to several
types of farming systems, the influences of which
on the landscape, could be interesting to
investigate.
3. The influence of the large growing city of
Kaduna on the nearby rural landscape may be worth
studying.
4. The area is covered by 1 : 25, 000 scale
aerial photography. Other areas, perhaps more
suitable, are not so well provided for.
5. The Kajuru area is the site of the annual
departmental survey camp and is therefore
convenient and accessible for fieldwork.
3. SOURCE MATERIAL
3.1 The test area is covered by three generations
of aerial photography flown at medium scale in
1950, 1'962, and 1972. Maps are also available at
1/50,000, 1/100, 000 and ' 1/250,000 scales,
prepared from the 1962 photography. For this
project the 1962 photography was not used directly
because it is of a smaller scale (1/40,000) than
that of other years and there would have been
problems caused by the varying scales and the
possibility of features recognisable on the other
photography not being visible.
3.2 1972 photography
This photography was taken by Renting Africa
