CREATE TABLE table_21933 ("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 1966 groundstation
SELECT COUNT("slope length") FROM table_21933 WHERE "elevation groundstation" = '1966'
SELECT COUNT("slope length") FROM "table_21933" WHERE "elevation groundstation" = '1966'