CREATE TABLE table_21935 ("Name or route" TEXT, "type" TEXT, "elevation groundstation" FLOAT, "elevation mountainstation" FLOAT, "slope length" FLOAT, "capacity in persons/hour" FLOAT, "construction year ( s ) " TEXT)

Name the slope length for gondola
SELECT MIN("slope length") FROM table_21935 WHERE "type" = 'gondola'
SELECT MIN("slope length") FROM "table_21935" WHERE "type" = 'gondola'