Migrants' routes cover the main geographical routes from tropical Africa towards Europe taken by people attempting to gain residence and work opportunities unavailable in their home countries. Although most migrants have Europe as their intended destination, alternative routes are also directed towards South Africa and Asia. Very few African migrants have European travel visas, therefore their only accessible way northwards is that of traveling along trans-Saharan routes and taking boat journeys across sea barriers. About 10% of the whole migratory stream uses sea routes.