Abstract
This paper presents an analysis of four open-source Global Digital Elevation Models (GDEMs) and compares them on two topographic profiles (nearly flat, and hills regions) for mapping and geomatics applications. The chief intention is to investigate if GDEMs-based heights, contour intervals, slopes, and topographic profiles are valid for all map scales of topographic mapping, which constitutes a major issue in mapping activities. Two case studies, the Nile delta in Egypt and Makkah city in Saudi Arabia, have been utilized to represent flat and moderate-topography patterns. The investigated GDEMs include the most-recent released models: ASTER v.3, ACE 2, SRTMGL1 v.3, and NASADEM_HGT v.1 released in 2019 and 2020 with spatial resolutions of 1 and 3 arc seconds. Available accurate Ground Control Points (GCP) consist of 540 stations in the Nile delta and 175 stations in Makkah. Based on the available datasets in two study areas, it has been found that the accuracy of investigated GDEMs over known checkpoints ranges from ±2.5 and ±5.1 meters in the Nile delta region, while it varies between ±5.1 and ±8.0 meters in the Makkah area. That indicates that the utilization of GDEMs in topographic mapping differs significantly between flat and hilly spatial regions. Therefore, it is recommended to avoid using GDEMs for developing topographic maps of scale 1:25,000 or larger in flat regions and map scale 1:50,000 or larger in hilly regions. Additionally, the accomplished results showed that all GDEM-based slopes do not match with the actual slopes from known GCP over cross section’s length up to 30 kilometers. Thus, it is concluded that GDEMs are not the appropriate heights’ source for topographic mapping at medium and large map scales, and could not be utilized for topographic profiling in precise engineering and geomatics applications.
Highlights
Topographic maps represent a chief type of maps utilized in numerous geomatics applications, such as engineering projects, hydrological modelling, disaster risk assessment, geomorphological and hydrogeological analysis, and environmental applications
Based on the available datasets in two study areas, it has been found that the accuracy of investigated Global Digital Elevation Models (GDEMs) over known checkpoints ranges from ±2.5 and ±5.1 meters in the Nile delta region, while it varies between ±5.1 and ±8.0 meters in the Makkah area
That indicates that the utilization of GDEMs in topographic mapping differs significantly between flat and hilly spatial regions
Summary
Topographic maps represent a chief type of maps utilized in numerous geomatics applications, such as engineering projects, hydrological modelling, disaster risk assessment, geomorphological and hydrogeological analysis, and environmental applications. Contour lines represent a vital piece of information that appeared on printed and digital topographic maps. They represent the terrain topographic variations and enable estimating heights of required random points. Geographic Information Systems (GIS) enables handling, processing, and analyzing DEMs to generate many forms of mapping terrain topography including generating contour lines for a wide range of applications Some of such applications include the production of flood hazard maps [1], mapping of geological structural lineaments [2], analysis of fluvial landscape in mountainous regions [3], monitoring impacts of sea level rise [4], the production of topographic maps [5], and geoid modelling [6]
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