Contouring a Kingdom

In another first for AOC, as part of The AAM Group, the Kingdom of Lesotho has been mapped.

Lesotho is a small, independent nation 3,055,063ha in size. It is known as “the Mountain Kingdom”, with many peaks over 3000m, and the highest “low” point of any country in the world at 1433m. Geographically, most of Lesotho is a high mountain plateau, carved out by river valleys. The lowlands are the area between the first range of mountains and the Mohokare River. The area between the first range of mountains and the eastern border is known as the highlands. A striking feature of the Lesotho landscape is the lack of trees. The country consists mostly of grasslands with woody shrubs.

The Department of Land Surveys and Physical Planning requested 2m contours across the lowlands and 20m contours across the highlands of the country. This was achieved in two parts – one part via aerial photography and one part via satellite imagery. Existing photography, captured by AOC, was used to create a Digital Elevation Model (DEM) across the lowlands. The data was subsequently manually edited and contours created. In addition, AOC captured the capital Maseru with LiDAR and provided 0.5m contours, a digital terrain model and a 13cm resolution orthophoto.

The highland contours were generated through the use of triplet sets of satellite imagery. The Japanese Advanced Land Observing Satellite (ALOS) captured stereoscopic images along the satellite’s track which were best suited for high resolution DEM generation. The coverage of ALOS was incomplete, so a single strip of SPOT 5 DEM was merged to create a comprehensive terrain model. The AAM Group generated a DEM from the ALOS data and subsequently contours across the highlands were created. Considerable time was spent ensuring that the data was consistent between the lowland and highland mapping. The data was checked for accuracy via a series a ground control points collected across the country. Results confirmed the project was within specification.

Chief Surveyor of the Kingdom of Lesotho, Mr Matela Motlotlo welcomed delivery of a new PC containing both lowland and highland datasets compatible with ESRI™ ArcGIS 9.2 along with a LiDAR dataset covering the Lesotho capital, Maseru. A plot measuring 1.5m by 3m was presented to the Minister for Local Government and Chieftanship, the Hon. Dr. ‘Matumelo Ponts’o Sekatle. As part of AOC’s commitment to providing solutions, a return visit is scheduled to conduct training in the use of the dataset within the ESRI environment.

Above: Leon Kettles (left) presents Chief Surveyor Mr Matela Motlotlo with the data