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INTRODUCTION 
The Regional Centre for Training in Aerospace 
Surveys (RECTAS), lle-Ife, Nigeria has the mandate 
to undertake research and consultancy services in 
mapping techniques in order to enable its training 
staff enrich their knowledge and experience which will 
be applied to the Centre's main function of Jong term 
training in the applications of aerospace surveying 
techniques (Photogrammetry, Remote Sensing and 
Cartography) for economic development and 
environmental protection in the African countries. In 
line with this policy, RECTAS welcomed a 
consultancy job offered to it by the United Nations 
Centre for Human Settlements, UNCHS (Habitat). 
The job involved map-revision and production of a 
‘Working Base Map’ for the sustainable Ibadan 
Project (SIP) in Oyo State of Nigeria. This project is 
one of the 12 world wide demonstration city projects 
for SCP under UMP, the principal goal of which is to 
provide planners and managers with improved 
capability to deal with the challenges of sustainable 
urban development. 
Ibadan is approaching a mega city with its population 
approaching $ million. It is a sprawling city covering 
approximately 450km?, located in the south-western 
portion of Nigeria; and geographic location for 
exactness is Longitudes E3?47'30" to E4?02'30" and 
Latitudes N7*17'30" to N7?32'30". By all standards it 
has a full representation of all the development 
problems associated with urban sprawl of a 
developing economy. Its immediate problems have 
been listed in a resolution passed by the City Forum 
held in October 1995 in Ibadan. The specific 
problems mentioned in the declaration were: 
development of a comprehensive metropolitan plan, 
property identification, protection of urban water 
sheds, establishment of an environmental 
management information system, including hydro- 
geological surveys, neighbourhood upgrading, 
drainage and flood control, environmental education 
and use of media, urban poverty, street trading, 
transportation and air pollution. Its immediate cross- 
sectoral problems are water-management, water 
supply and institutiona-lization of the Environmental 
Planning and Management process (SIP, 1995). 
The UNCHS (Habitat) recognises that an accurate, 
up-to-date and reliable topo-map and digitized 
Working Base Map will initiate a move into the digital 
technology and a subsequent cross-sectoral use of 
the tools of Geographical Information System (GIS) 
for the long term management goals of SIP. 
19 
The Working Base Map, therefore, appeared to be 
sine qua non basic requirement of the SIP. It was 
planned at two scales: (i) a global series at 1:50,000 
scale in one sheet, covering virtually the entire 
metropolitan area comprising of five municipal local 
governments and six peri-urban Local Governments; 
(ii) a sector series of 4 map sheets at 1:25,000 
containing relatively more detailed information for 
local government level planning, particularly in the 
core areas of Ibadan. 
To produce the two scale series, there was the need 
to evaluate and select from the existing topographic 
maps over Ibadan, the most appropriate to be used 
as the base. 
MATERIALS AND METHODOLOGY 
For the job, the UNCHS (Habitat), Nairobi, Kenya, 
supplied a quarter scene SPOT P data stored on CCT 
and a hard copy photographic product. RECTAS 
supplemented with a full scene SPOT XS, the latter to 
cover as much as possible the parts of the 
metropolitan region not covered by the quarter scene. 
The map revision and digital production spanned over 
the following phases: survey of map situation at 
Ibadan for base map selection and identification of 
map producers and users in the city; processing of the 
satellite data and interpretation of the imageries; 
ground truthing for rectification of existing map 
information and image interpretation; field editing, 
overlaying for transfer of image interpretation onto the 
map transparency (compilation); field editing for 
correction of place names, scribing of the compilation 
and photographic reproduction in transparent copies 
of the layered information, and finally the digital 
production of the layered information on digital files. 
Map Situation Survey and Base Map Selection 
It would appear that between 1918 and 1990 about 
sixteen topographical maps have been produced, yet 
there still exist information gaps - spatial gaps and 
temporal gaps (RECTAS SIP Report, 1996). 
Out of the sixteen series, copies of some of which 
could not be available to be procured, two series were 
selected as the most appropriate base for the 
compilation of the Working Base Map. These were 
the 1:50,000 national series compiled nation-wide 
between 1964 and 67 (Fed. Surveys, Nigeria; 
Canadian Aerospace Services, 1964/1967) and a 
special project mapping for the Water Corporation of 
Oyo State, Nigeria, (Ogunleye/Geosystems, 1990) 
commis-sioned to be produced at a scale of 1:10,000. 
The latter covers the municipality only while the 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996