The data from the Swiss region used in some examples is taken from two sources.
The SRTM page offers the interface to select the zone. In this case, the zones are srtm_38_03 and srtm_39_03.
To merge the zones and downscaling the resulting image, I resulting
gdalwarp -te 5.7 45.7 10.7 47.9 -ts 1000 0 *tif swiss.tiff
Which will create a width=1000 pixels image.
The border of switzerland is taken from this project: https://github.com/interactivethings/swiss-maps
Clone the project and run:
make topo/ch-country.json REPROJECT=true