Topographical Map Updating Using Sentinel 2A

Effective and efficient decision making and development planning requires fundamental geo-spatial information collected and maintained in a systematic approach. At the national level, this fundamental information is usually obtained from topographic maps. The rapid changes due to physical developments in the so called 'African small towns' has in the recent past re-oriented the attention of the mapping institutions to search for a faster and more economical map revision approaches. This study reveals one among other possible methodologies that can similarly be tested to assess their efficacy in providing local solutions in the mapping industry. Its primary focus is promotion of freely available high resolution satellite data in updating old topographical maps. The focus area is Konza topographic map (a sampled small town in Kenya), sheet number 161/2.

The "latest" Konza topographic map at a scale of 1:50,000 was published by Survey of Kenya in 1961 from aerial photography of 1948. This study noted that the information contained thereof, relative to the current ground analysis misleads more than informs. Apart from a few settlements in Muongoni, Ngiini, Kyamutheke and a few shops around Konza village, vast areas under the description under sheet number 161/2, are empty in terms of human habitation. Accordingly, it is noted that land utilization as described by the old map, is predominantly ranching. Existing literature also reveals that besides Konza, there is an extended 'neglect' in keeping African maps current. This research attempts to nullify some of the assumptions taken as reasons for the poor state of Africa maps and also to negate the notion that a donor must appear for a map to reappear.

The methodology is easily replicable, starting from scanning of the repromats, creation of a geodatabase, cleaning the vectorized datasets from the old map and integrating the existing information from the old topographic map with the new information derived from the satellite imagery. Preliminary ground truthing was obtained from Google earth and filed completion carried out. An updated topographic map of Konza was the main deliverable. Quality assessment was mainly by visual inspection of the overlays and adherence to acceptable root mean square error (RMSE) according to map scale.