Accuracy Assessments of Geographical Line Data Sets, the Case of the Digital Chart of the World

To be able to utilise geographical data for analysis, one should know something about the quality of the data. In present geographical data standardisation proposals (SDTS, CEN TC287), several aspects of geographical data quality have been described, such as lineage (data collection and processing history), spatial accuracy, attribute accuracy, completeness, logical consistency and currency. Methods for quantitative assessments of different aspects of spatial accuracy for data sets of linear geographical features, such as shape fidelity and positional accuracy are described. For these assessments, independent data sets of better (and preferrably known) accuracy will have to be used. In order to be able to do automatic assessments, data set completeness must be taken into consideration. The method has been applied for assessing the spatial accuracy for some themes of the Digital Chart of the World (DCW) (scale of original maps (ONCs): 1:1000000), using the Norwegian mapping authority’s national N250 map series (scale 1:250000) as a reference data set.