TopOSM is an OpenStreetMap-based topographic map, similar in style to the USGS and National Geographic topographic maps.
A topographic map is a kind of map which uses contour lines or other ways to show elevation and topography.
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Text based on Wikipedia,
License: TopOSM by Lars Ahlzen | Map data: © OpenStreetMap Contributors, USGS | CC-BY-SA 2.0