Ski orienteering is a form of cross-country skiing competition that requires navigation in a landscape, making optimal route choices at racing speeds. Standard orienteering maps are used, but with special green overprinting of trails and tracks to indicate their navigability in snow; other symbols indicate whether any roads are snow-covered or clear. Standard skate-skiing equipment is used, along with a map holder attached to the chest. It is one of the four orienteering disciplines recognized by the International Orienteering Federation. Upper body strength is especially important because of frequent double poling along narrow snow trails.