Both data sources allow you to download specific tiles of your location, that means I already got the "slices" I need. ArcMap previews these files correctly (depending on the file which was imported first). However, clipping the exact study area leads to errors, this is why I was trying to change the projection of the elevation model. I would like to project a new file but the tool does not allow me to take the .tif. The file is not available throught the file browser of ArcMap. I hope I understood your instructions.
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