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Transformation of Census Cartography from a conventional
paper map system to an integrated Geographical Information
Technology based system in African Countries – A private
sector perspective with specific reference to Namibia
3. Conventional approach to census cartography
The purpose of the cartographic (sub-) project of a census is to provide the geographical
framework for the enumeration phase. Census cartography therefore deals with the systematic
subdivision of a country or study area into a contiguous mosaic of small pieces of land, each
big enough in terms of population and area, to be manageable by one enumerator during the
enumeration phase. These pieces of land are usually referred to as enumeration areas (EAs)
and the process is known as (EA) demarcation. The lowest level of reporting of census results
determines the geographical framework of a census. Census demarcation therefore usually
adheres to the political and administrative boundaries in a country. The most important
deliverable of a cartographic project is a set of detailed enumeration area and supervisor area
maps. A supervisor area usually consists of three to five adjacent EAs and is mainly used for
management purposes during the enumeration.
In order to produce the required maps, a census office would first of all obtain all available
base maps from the official mapping authority of its country. The maps include 1:250 000 and
1:50 000 topographical maps; town maps and cadastral maps for the country, as well as any
other maps that might be useful for the project. In most African countries the acquisition of
maps immediately reveals the single biggest problem facing a census cartographic team: the
lack of current maps. Since the size and geographical spread of the population of a country is
critical for census preparation work, the lack of detailed current base maps poses an immense
challenge to census mapping experts.
In Africa, in general, most of the topographical maps are 20 years and older. A significant
portion of topographical maps was last updated before 1970, which makes them older than 30
years. The population size of most countries on the continent more than doubled over the last
thirty years. This fact, together with massive internal and international migration makes the
use of the available topographical maps extremely difficult and undesirable. The same
problems also apply to town maps. It can therefore be argued that currency and, to a lesser
extent, lack of detail are the biggest problems associated with the maps available for census
purposes.
The solution has been to make use of sketch maps in cases where no maps are available or in
cases where the available maps do not meet the mapping requirements for a census. Census
demarcation fieldworkers are trained to sketch enumeration area (EA) boundaries, as well as
certain prominent features within an EA. In recent censuses the sketch map methodology had
been combined with Global Positioning Systems (GPS) technology where GPS receivers were
used to geo-reference the sketch maps. In some instances, depending on the settlement pattern
and population density, the 1:50 000 or even 1:250 000 topographical maps remained the only
useable maps for census demarcation and therefore had to be used. In urban areas available
maps were also enhanced / complemented by sketch maps.
The mentioned approach was, until recently, the only viable option available to census
projects and was hence considered to be the best solution under the circumstances. There is,
however, numerous so-called errors of coverage associated with the use of an inferior base
map, making census practice in African countries both difficult and inaccurate. Errors of
coverage deals with all errors associated with the missing of certain individuals or
households, as well as the double counting (or more than double counting) of persons or
households in a census. Although most of the errors usually occur during the actual counting
process (enumeration phase) a number of significant errors can be directly ascribed to
deficiencies in the cartographic base of a census. Since there is often little or no available
information on the size and spread of the population prior to the cartographic fieldwork, it is
extremely difficult to plan the work properly. It is also very difficult – if not impossible – to
check the work done by field teams without physically revisiting the areas in the field. A
census cartographic team thus has to rely on the output from the field without really having
any control over the quality and coverage of the work. It is often also very difficult to locate
the exact position of administrative political boundaries on the ground. The reason for this
being the fact that many of the boundaries were defined by using maps that were already
dated at the time the boundaries were changed / proclaimed. The result is that the position of
an administrative boundary is often expressed in terms of coordinates and hence they often do
not follow features on the ground. This makes it very difficult to locate these boundaries on
the ground and hence often leads to demarcation and enumeration coverage errors. Most of
the mentioned issues are a direct result of the inherent deficiencies of the conventional
methods used for census cartography. It can therefore be argued that, if applied properly, GIT
should improve the quality of censuses through, amongst others, better quality maps.
4. GIT approach to census cartography
The unique spatial data needs for censuses make a census an ideal candidate for GIT
solutions. The key is not to use technology merely for the sake of technology, but to use
relevant technology that provides workable solutions.
4.1 The use of GIT in the creation of base map data
As already mentioned, most available base map data (hard and soft copy) relevant to censuses
in developing countries are dated. A huge demand for base map data thus exists and could be
addressed on two distinct levels of detail, namely satellite imagery and high-resolution digital
aerial photography. The progress in the field of digital base map data collection and image
processing over the last few years has been nothing short of spectacular. Due to the
availability of sophisticated image processing software combined with powerful and large
capacity computers, both these data sources nowadays provide a sound and viable base map
data solution for the building of a GIS. Satellite image analysts can, with modern image
processing techniques, determine the size and relative density of all populated areas within a
selected country or area of study from satellite data obtained from satellites such as SPOT or
Landsat. This data can then be used to determine the exact areas for which high resolution
detailed digital aerial photography is required. Detailed base map data generation through the
use of modern digital aerial photography systems can then be focussed on the exact areas
where required. Modern digital aerial photography systems, such as the Finnish system being
utilised by GeoSpace International, provide high-resolution digital colour imagery at a
fraction of the cost of conventional aerial photography. It also has the added advantage of an
extremely short image processing time compared to conventional aerial photography.
4.2 The use of GIT in census EA demarcation fieldwork
The main aim of census demarcation fieldwork is to define EA boundaries. This is normally
done after the necessary base map data has been obtained from the relevant sources or created
through the most relevant method for a given area. Although there is currently no real
substitute for census demarcation fieldwork in the African context, GIT can make the task far
more efficient through better control and better management. By having access to more
detailed and current base map data, the fieldwork exercise can be better planned and
managed. Maps at the required size, level of detail and scale can be generated to optimise
fieldwork. The data collected in the field can also be captured in the spatial data base. To
minimise coverage errors, fieldwork outputs can furthermore be checked against the external
sources of data, such as satellite imagery. Once the data collection at all levels is completed,
maps that meet the exact requirements of the different levels of census management, can be
generated.
4.3 The use of GIT in map production
GIT enables one to produce maps at various sizes, scales and levels of detail for each unique
requirement. Over and above the fact that one has the flexibility to produce a map for every
situation, you furthermore has the ability to develop map printing applications that enables the
production of literally thousands of similar maps using standard map layouts and criteria over
a relatively short period of time.
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