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Addressing the challenges associated with census mapping in Africa
3.1 User needs
The information age that we are current living in places more and more demand on the need for digital spatial data. This is also the case in Africa. Furthermore the need for quality and relevant statistics for developmental planning purposes is bigger than ever. A statistical agency therefore has to adjust in order to the respond to the spatial data needs of their users. Some statistical agencies are currently responding to user needs by using Geographical Information Systems (GIS) in post-enumeration activities (only). Although this is a step in the right direction it is argued that more emphasis should be placed on the use of GIS and geographical information technology (GIT) in pre-census activities. In doing so the platform for small-area (spatial) census data products are created as a direct deliverable of the methodology.
3.2 Advances in technology
GIT has advanced by leaps and bounds over the last few years. The processing power of computers and software packages are increasing by the day. Moreover, the integration and utilisation of GIS, GPS and remote sensing are also becoming easier and more cost effective. There can be no doubt that the right tools exist and it has never been easier to utilise these tools in geospatial applications. It is argued that, if implemented as part of a population and housing census project, the technology is now within the financial reach and technical capabilities of most statistical agencies in Africa.
3.3 The cost factor
Although the initial financial layout required for the establishment of a GIS Office at a statistical agency is still relatively high it is a much more affordable exercise than say ten years ago. Furthermore, if applied optimally, a statistical agency can recover the initial capital layout of the GIS infrastructure from the savings in the mapping sub-project of the first population and housing census that will benefit from the technology. This is made possible mainly by significant savings brought about by streamlining the pre-enumeration census demarcation fieldwork exercise.
3.4 Capacity building
The future of census mapping is digital. All developed countries are already using it. The sooner all statistical agencies starts building the required capacity the better since international standards and the overall demands driven by the information age will eventually demand statistical agencies to do so. It must be mentioned that building the required capacity is nowadays much more realistic than before since the technology (GIS, GPS, satellite imagery, digital aerial photography, etc.) is a lot easier to use and integrate than before.
3.5 The issue of quality
If digital census mapping is applied correctly and optimally it is guaranteed to provide better quality results when compared to conventional mapping. The normal errors associated with census mapping such as incomplete coverage or double coverage of the same area is to a large extent eradicated.
3.6 International trends:
The United Nations (UN) [1] are promoting the use of GPS, Digital Imagery and GIS with Census Mapping. It can therefore be expected that more countries will be encouraged and empower by the UN to implement digital census cartographic methodologies in the 2010 round of censuses.
4. Modern (GIT) methods
Modern methods assume the optimal utilisation and integration of GIT tools. GIT tools include: GIS (including desktop GIS, mobile GIS and WEB GIS); GPS; remote sensing (satellite imagery and digital aerial photography).
It is important to understand the technical capabilities of current GIT tools, but it is also important to keep in mind that the crux of the matter is really the optimal integration of the available tools in order to arrive at the best possible solution for a given country. Experience has shown that no two countries have/will have the same solution. This is due to the fact that countries are unique in terms of the combination of variables that dictates the optimal solution that can be realistically implemented. These variables include population size, population distribution, settlement patterns and densities, geographical area, availability and specifications of base maps, agency capacity with regards to GIT, the census mapping budget, timeframe for implementation and commitment to the transition from conventional to modern census mapping methods at senior management level. If these factors are not taken into consideration and the available tools are not optimally used and integrated as part of a total census mapping solution it could easily become more of a hassle to the census cartographer than an aid.
4.1 Technical capabilities of GIT tools
GIT tools have developed tremendously over the last decade whilst at the same time becoming more and more affordable. GIS software and hardware is much more powerful, flexible and easier to use than was the case a few years ago. GPS receivers are more user-friendly and communicate elegantly with most GIS platforms. Mobile GIS with integrated GPS provides so-called “moving maps” that enable fieldworkers to navigate with relative ease to an area to collect spatial and attribute data. Electronic forms eliminate the need for paperwork. WEB-GIS is becoming more and more popular for census and survey operational management as well as dissemination of all statistical data with a geographic link.
Remote sensing in census and survey mapping is not Remote sensing (satellite imagery and digital aerial photography (DAP)) nowadays enables the census cartographer to have access to a GIS-ready base map for an entire country that meet all the needs of the census (i.e. currency, accuracy and level of detail). This technology enables the census cartographer to have a detailed base map for the entire country that is less than two years old thus eliminating the problems associated with dated base maps. This base map is suitable to be used as the base map for enumeration area and supervisor area maps. Because of differences in population characteristics (mainly geographic spread and densities) in urban and non-urban areas there are different base map solutions for urban and rural areas.
4.2 Rural base map: the SPOT5 solution
SPOT5 is the first commercial satellite that provides a feasible base map solution in terms of specifications and cost for census mapping purposes at a national (total coverage) level. The latest SPOT5 2,5m (pixel resolution) natural colour satellite imagery in particular provides the ideal base map for rural and even less dense urban areas. The technical specification of the imagery, as well as the ability of the satellite to do image acquisition of vast geographical areas such as national coverage’s linked to fast image processing capabilities ensuring relatively short delivery schedules, makes it an attractive option for census mapping purposes. Although still costly it is within the census mapping budget of most countries – especially if one takes into account the huge savings that can be made in reduced EA demarcation fieldwork as a result of the inherent benefits of having a detailed base map.
SPOT5 5m natural colour imagery is lower resolution product from the same satellite. It is significantly cheaper than SPOT5 2,5m but there is an obvious compromise in terms of pixel resolution. A major advantage of SPOT5 5m is that the archive coverage on this product is, for most parts of the world, much more extensive than is the case with the SPOT5 2,5m archive. The archive imagery is cheaper than the programmed imagery and it takes the risk out of programmed image acquisition. Programmed image acquisition is determined by prevailing weather conditions as well as the priority of a given image acquisition project in relation to other projects at a given point in time. This is due to the limitations on the onboard storage capabilities of the satellite. SPOT Image is however currently the only satellite company that provides the client with a feasibility study prior to ordering the imagery.
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