An analysis of almost 200 references has been carried out in order to obtain knowledge about the DEM (Digital Elevation Model) accuracy assessment methods applied in the last three decades. With regard to grid DEMs, 14 aspects related to the accuracy assessment processes have been analysed (DEM data source, data model, reference source for the evaluation, extension of the evaluation, applied models, etc.). In the references analysed, except in rare cases where an accuracy assessment standard has been followed, accuracy criteria and methods are usually established according to the premises established by the authors. Visual analyses and 3D analyses are few in number. The great majority of cases assess accuracy by means of point-type control elements, with the use of linear and surface elements very rare. Most cases still consider the normal model for errors (discrepancies), but analysis based on the data itself is making headway. Sample size and clear criteria for segmentation are still open issues. Almost 21% of cases analyse the accuracy in some derived parameter(s) or output, but no standardization exists for this purpose. Thus, there has been an improvement in accuracy assessment methods, but there are still many aspects that require the attention of researchers and professional associations or standardization bodies such as a common vocabulary, standardized assessment methods, methods for meta-quality assessment, and indices with an applied quality perspective, among others.

Abstract:We have carried out a characterization of users and uses of Digital Elevation Models (DEMs), in order to be able to study an adaptation of the most appropriate DEM. In the previous literature, there have not been many similar studies of this subject. We used information about DEMs downloaded from a Download Center of a National Mapping Service (in this case the Centro Nacional de Información Geográfica, CNIG, of Spain). This service offers three DEM products with different spatial resolutions (DEM05, DEM25 and DEM200). We employed a total of 12,493 records from an online survey. The completion of the survey was mandatory at the time of the download (year 2014). We determined the geographical location of downloads, the profile of users, the use of the DEMs and the user assessment. We identified 6087 different users, most with a profile of private professionals (71%) and related educational activities (18%). Most of the users performed only one download. The major uses are those related to teaching-research and professional activities. Uses related to leisure, sport and tourism were 9.5% of all cases. The valuation performed by users of the utility of the products was very high, but not particularly in relation to updating needs.

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There are many studies related to Imagery Segmentation (IS) in the field of Geographic Information (GI). However, none of them address the assessment of IS results from a positional perspective. In a field in which the positional aspect is critical, it seems reasonable to think that the quality associated with this aspect must be controlled. This paper presents an automatic positional accuracy assessment (PAA) method for assessing this quality component of the regions obtained by means of the application of a textural segmentation algorithm to a Very High Resolution (VHR) aerial image. This method is based on the comparison between the ideal segmentation and the computed segmentation by counting their differences. Therefore, it has the same conceptual principles as the automatic procedures used in the evaluation of the GI’s positional accuracy. As in any PAA method, there are two key aspects related to the sample that were addressed: (i) its size—specifically, its influence on the uncertainty of the estimated accuracy values—and (ii) its categorization. Although the results obtained must be taken with caution, they made it clear that automatic PAA procedures, which are mainly applied to carry out the positional quality assessment of cartography, are valid for assessing the positional accuracy reached using other types of processes. Such is the case of the IS process presented in this study.