Evaluating the Potential of Opensource Geospatial Data in Topographical Map Revision

Abstract

Topographical maps are general reference maps that depict the planimetric position of both natural and manmade features and the general terrain. In Kenya topographical map-making dates back to the colonial period when the Directorate of Overseas Surveys was mandated to carry out and regulate all the mapping activities in the country. These topographical maps were produced and revised using the conventional method of topographic map making. This process took a couple of years to conclude, it was labor-intensive and the overall cost of the project was very high. This explains the slow pace with which topographical map production and revision is being carried out in the country. Geospatial advancements both software and hardware for data collection and processing has greatly improved the quality of geospatial products and significantly reduced the processing and production time. The continued improvement in the quality of satellite imagery has seen many National Mapping Agencies Cross the world use satellite imagery as an alternative source of data in compilation and revision of topographical maps. In Kenya SPOT high resolution satellite images was used in 1996 to revise the 8th edition of SK topographical map sheet Numbers: 148/1, 148/2, 148/3 and 148/4 covering the general area of Nairobi. Developments in web technology have had a great contribution in the field of geospatial and have continued to evolve to improve map user’s experience. Web 2.0 which allows users to create and share content online has led to the general growth of crowd-sourced data and Volunteered Geographic Information in the geospatial sector. National Mapping agencies across the world are putting in place systems to take advantage of these developments. This study aimed to evaluate the potential of Opensource geospatial data in topographical map revision. Planimetric and elevation data quality specifications required for the revision of SK topographical map at scale 1:50,000 was reviewed. Vector datasets from OpenStreetMap were downloaded and assessed in terms of geometric accuracy, attribute accuracy, and completeness. The research has provided means by which incompleteness in the OSM data can be addressed using open-source satellite imagery available in OSM. OSM imagery has also been used to visually validate the geometric accuracy, attribute accuracy and completeness of the OSM data. The roads, building and vegetation datasets were identified for evaluation. After evaluation process it was clear that only the roads dataset met the data quality requirements needed for the compilation or revision of SK topographical map at scale 1:50,000. The elevation dataset derived from SRTM V3 was also evaluated and found to be suitable for revision of Nairobi topographical map sheet No. 148/4. Cartographic processes of generalization and symbolization were then applied to the vector data and this was used to present the open-source source datasets that met the standards required for SK topographical map revision.