For reasons not entirely clear to me, the German word Gelände (terrain, area, grounds...) became the Japanese term for ski slope, as illustrated by this gerendemappu. As usual with Japanese, the word suffered somewhat in the adaptation process.
My thanks go to Bettina Ortmann for pointing gerende out to me and to Stefano Suigo for finding the gerendemappu for me.
The picture is from http://www.nozawaski.com/winter2011-12/course/map.php.