Comparison of Methods for Deriving a Digital Elevation Model from Contours and Modelling of the Associated Uncertainty

Anicet Sindayihebura 1, Marc Van Meirvenne1 and Stanislas Nsabimana2
1 Department of Soil Management and Soil Care, Ghent University
Coupure 653, 9000 Gent, Belgium
Tel.: + 32 (0)9 264 6056; Fax: + 32 (0)9 264 47
anicet_fr@yahoo.fr; marc.vanmeirvenne@ ugent.be
2 Department of Geography, University of Burundi
P.O. Box: 1550 Bujumbura, Burundi
Tel.: + 257 244006; Fax: + 257 22 3288
snsabim@yahoo.fr

Abstract
Topographic maps are the most  common sources of Digital Elevation Models (DEMs).On these maps elevation data are explicitly displayed along contour lines. However such an input is not fully representative of the terrain shape which is known to vary continuously and smoothly in space. Moreover, in many instances the DEM is not the final objective. In our case, we intend to use it along with its derivatives as secondary information in interpolation of soil attributes. So DEM errors will propagate into the target variable. Therefore assessment of the amount and spatial distribution of these errors is crucial. Often, what is important is not the absolute DEM accuracy but the reproduction of the terrain shape. In this respect quantitative assessment criteria should be complemented by other qualitative criteria that account e.g. for artefacts and inconsistencies. The topographic data source is an 1:50000 topographic map with a 20 m contour interval. The study area has an area of 14.8 km2  and is composed of two contiguous watersheds located in a mountainous and lithologically contrasting zone of Burundi. Correlations between soil attributes and DEM-derived topographic attributes are significant, but they are too weak to be readily accounted for in soil attributes interpolation. Also propagation of DEM uncertainty into DEM derivatives is too pronounced and precludes the use of these as  secondary information  in soil attributes interpolation. Therefore we suggest changing the DEM into topographic units and use these as well as lithologic units as categorical soft information.   

Keywords: Digital Elevation Model, correlation, interpolation, uncertainty

In: Caetano, M. and Painho, M. (eds). Proceedings of the 7th International Symposium on Spatial Accuracy Assessment in Natural Resources and Environmental Sciences, 5 – 7 July 2006, Lisboa, Instituto Geográfico Português

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