MAPPING WITH SPOT SATELLITE IMAGERY: THE NIGERIAN EXPERIENCE
Dr. Olusola Atilola
Sola Atilola Associates
116 Obafemi Awolowo Way,
P.0. BOX 7585,
Lagos State
Nigeria
Ikeja,
Commission IV
ABSTRACT
This paper reviews the state of topographical maps in Nigeria vis-a-vis the status of world mapping at
1:50,000.
Application of SPOT Satellite imagery for the production of 1:50,000 planimetric maps of areas
not covered by the existing conventionally produced maps at this scale is presented.
Methods of production, revision and metrication of parts of the national topographical
maps using SPOT Satellite imagery are also presented.
KEY WORDS:
1. INTRODUCTION
Topographical maps are the basic prerequisite for
any meaningful planning, development and effective
management of the natural resources of any nation.
However the recent research conducted by United
Nations Organisation (UNO) and reported by Braden-
berger et al (1985), shows that only about 42% of
the world land area is covered by basic 1:50,000
map series and these maps are revised at the rate
of only 2% per annum. The developed countries of
the world are the best mapped with Europe and North
America having a coverage of 91% and 61% respecti-
vely, while Africa and South America are only
mapped to 29% and 27% respectively. It is thus
apparent that there is a strong correlation betw-
een development and availability of medium scale
maps.
It has been estimated that using the conventional
photogrammetric method it will take not less than
40 years to achieve full coverage of the world at
1:50,000; while the rate of updating cannot be
less than every 40 years. It is thus apparent
that the mapping needs of the world especially the
developing countries, at a scale of 1:5000 and
smaller scales, are not being met today by the
conventional photogrammetric mapping operations.
However, the increase in spatial resolution of
commercial satellite images namely: Landsat MSS
(1972) Landsat TM (1982) and SPOT (1986) with
spatial resolution of 80m, 30m and 10m/20m respec-
tively is fast changing the realisation of the
mapping needs of the world at the 1:50,000 and sma-
ller scales.
2. THE STATE OF BASE MAPS IN NIGERIA
Nigeria has a land form area of about 1,000.000km.
The country is covered by about 1500 sheets of 1:
50,000 map series. Up till 1989 about 90% of the
country was covered at this scale. However,
through the mapping commissioned by the National
Population Commission (NPC), for the 1991 popula-
tion census, the whole country was covered by
December 1990. As laudable as this feat may seem
in comparison with UNO's research finding concer-
ning the state of world mapping, the question of
spatial fidelity and completeness of most of these
maps remain unresolved.
The early topographical maps of the country were
produced by approximate means which included tra-
cing from aerial photo, after control points have
been supplied by slotted templates; and later by
116
Mapping, Map Revision, Space Imagery, SPOT, Remote Sensing.
multiplex (Atilola,1986). Some of these
maps produced, before the use of topogra-
phical plotters in the fifties, with limi-
ted accuraces, are still being used today
without revision against the UNO's recomm-
ended revision period of 10 years for areas
of high human activities and 15 years for
remote areas.
Apart from the obsoleteness of the content
of these base maps, most of them are still
in imperial units and Modified Transverse
Mercator projection system while the count-
ry has changed to metric and UTM systems.
2.1 Need for the Application of Satellite Imagery
to Mapping in Nigeria.
As indicated above if the mapping of the remain-
ing part of the country at the basic 1:50,000
scale and the revision of the existing map sheets
at this scale were embarked upon using the conven-
tional photogrammetric method, it might take not
less than 40 years to complete. This is on the
assumption that the whole country could be covered
by the appropriate aerial photographs. From exper-
ience, production of high altitude photograph has
always constituted a bottle neck in the basic
mapping programme of Nigeria, as some areas in the
southern and middle belt of the country are under
cloud cover for most of the year. Therefore in
order to produce the 1:50,000 maps, of the remain-
ing 10% of the country that were urgently needed
for delineation of Enumeration Area (EA) in the
1991 national population census and meet the basic
mapping needs of the country the catographic appli-
cation of SPOT satellite imagery had to be applied.
Of all the commercial satellite, SPOT satellite is
unique because of the cartographic capabilities of
its products, the world wide coverage and the rela-
tive ease with which the products can be obtained.
Therefore in the remaining of this paper, the
catographic applications of SPOT products are
reviewed and the experience in the production of
1:50,000 maps for the National Population Commiss-
ion (NPC) using SPOT imagery is presented. Other
projects currently being carried out in the count-
ry as a result of the success of the NPC mapping
are also reviewed.
3. CARTOGRAPHIC APPLICATION OF SPOT IMAGERY
Various research work and practical applications
of SPOT and Thematic Aa Ve (TM) satellite image-
ries point to the fact that SPOT imagery can be
used fo
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