former is of nation-wide coverage and therefore
contains the whole of Ibadan and its environs.
The survey revealed improper records keeping and
co-ordination of the mapping activities in Ibadan as
well as apparent lack of awareness of mapping
activities.
Neither of the two base maps selected reflected the
rapid expansion of the city in the last thirty years. The
1:10,000 scale series which was compiled in 1990
covers only the inner city. The other base map, which
covers the entire metropolitan region, was however
compiled between 1964 and 1967 grossly outdated in
view of the rapid city expansion in the seventies and
eighties. The most effective source of information for
quick updating was the high resolution imagery of
SPOT P (10m, which could be sharpened to 7.5m),
and SPOT XS (20m, in three bands, which could be
composited in colours). The revision used the two
modes combination effectively.
As part of the SIP's principle of grassroots
consultation for “planning for the people by the
people", the map situation survey was not only for the
base map selection, but partly also to determine the
preferences of Ibadan actual and potential map users.
The survey was partly consultative with the result that
the global scale of the Working Base Map was
requested by the Local Government planning
authorities to cover all the eleven Local Government
secretariats of the Metropolitan area. The 1:50,000
map sheet was therefore a “special edition” with a
format of interior frame of the surface area being
73.5cm by 70cm and a print size of 93cm by 85cm.
The revised format accommodated all the eleven
Local Government Secretariats.
The preliminary draft of the map was exhibited in the
first city (consultation) forum held in Ibadan in
October 1995, to assess its acceptability by all stake
holders. It was well accepted and all the comments
made were accordingly incorporated for improved
accuracy and reliability of the final maps.
Processing of the SPOT Data for Updating the
map:
The SPOT satellite imagery data used were KJ
067/335, the P mode taken in December 1993 by
SPOT 3 and the SPOT XS-mode taken in December
1986 by SPOT 1. The P-mode data provided the
cartographic-precision information for the UTM
projection which was requested for as per Nigerian
national projection system specifications. The XS-
mode was useful for land use information and also for
20
areas not covered by the P data. The two data sets
were further processed from their CCT storage
medium. The digital image processing was performed
using the MULTISCOPE software on COMPAQ 486
computer system at the Remote Sensing Laboratory
at RECTAS. Subscenes of 20cm x 20cm format were
printed on thermal wax transparency and paper.
These were mosaicked to correspond with the sheet
size of the 1:50,000 scale series maps. The same
process was repeated for the 1:25,000 scale.
Interpretation and Ground Truthing
The aim of the spectral enhancement processing and
the interpretation of the enhanced images was to
obtain the relevant topographic and landuse
information conforming to and acceptable as the
standard 1:50,000 and 1:25,000 topographic map
series.
It has already been remarked that the revision was
effectively showing the zone of rapid urban expansion
during the last thirty years when the 1:50,000
topographic maps were compiled. The imageries
provided the main source of information for the
compilation of the roads, building densities,
vegetation and other land use and topographic
features. Although the geometric correction and pixel
resampling sharpened the spatial resolution much
higher to 7.5m instead of 10m, this improvement did
not resolve the problem of spectral confusion of some
topographic features. For example bare ground of
reddish soil confused with rusted roofs of the old
buildings; water and vegetation in the panchromatic
imagery often appeared in the same tone for areas
with moist conditions. There was extensive ground
truth to resolve the spectral confusion.
Field Editing
The map survey revealed that the existing topo maps
selected for the compilation did contain a
considerable number of wrong toponyms including
mis-spelling and misplacement of place names. The
corrections also demanded very extensive field
editing. Ibadan as a sprawling city has a massive
outer zone growth with characterization similar to the
blight of the congested inner zone of old and decayed
buildings. In addition, the housing of the outer zone
proceeded rapidly without proper consideration for
planned provision of common amenities and
infrastructures. The public buildings that exist are
mixed up together with the residential houses, making
it impossible to separate and annotate the former
directly with the imagery. Field pointing with
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
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