Niger's geographical location makes it a crossroads for trade between North Africa and sub-Saharan Africa. Located in West Africa between the parallels 11°37 and 23°33 north latitude on the one hand, and the meridians 16° east longitude and 0°10 west longitude on the other hand, Niger covers 1,267 000 km2. It is the largest of the West African countries and ranks 6th on the continental scale (after Algeria, the Democratic Republic of Congo, Sudan, Libya and Chad). Niger includes a southern zone with a Sudanian and South-Sahelian climate. North of the Filingué-Tahoua-Tanout line, it gives way to the North-Sahelian climate, then to the Saharan climate in the North, the Aïr massif and the plains that surround it. The relief of the country is quite varied. The Niger valley has a bed strewn with islands, bordered by basins, framed by sandstone cliffs. The southern regions present a tabular relief forming low lateritic plateaus, cut by depressions such as the Dallol Bosso and the Dallol Maouri, desiccated tributaries of the Niger: plateaus of the Damergou and the Ader, covered with a lateritic crust sinking the west under the middle Niger sandstones. The Azawad is a vast sandy plain, crossed by wide shallow valleys; the Aïr, a set of rocky massifs cut by narrow valleys where life is more active. The eastern part of the country, in the north of Chad, is a region of sand: it encompasses the great erg of the Ténéré, formed of sharp dunes interrupted by the clay depressions of the Kaouar and the Agram. The Niger enters the state to which it gives its name through the Labbézenga rapids. It receives only secondary tributaries (Gorouol, Sirba, Goroubi, Mekrou) and on the right bank only. The tributaries of Chad are of little interest to the country; the Komadougou Yobé forms, over 15 km, the border with Nigeria; it is only a thin stream. Included entirely in the Sahelian and Saharan climate zone, the country has two seasons, dry and wet, clearly differentiated; precipitation decreases towards the north.