Chad Basin British and French concluded an agreement to clarify the boundary between French West Africa and what would become Nigeria. A boundary was agreed along a line from Say on the Niger to Barruwa on Lake Chad, but leaving the Sokoto Caliphate in the British sphere. Parfait-Louis Monteil was given charge of an expedition to discover where this line actually ran. On 9 April 1892 he reached Kukawa on the shore of the lake. Over the next twenty years a large part of the Chad Basin was incorporated by treaty or by force into French West Africa. On 2 June 1909
Nigeria (), Niger (), Chad (), Cameroon (), and has a coastline of at least s. Nigeria lies between latitudes 4° and 14°N, and longitudes 2° and 15°E. The highest point in Nigeria is Chappal Waddi at . The main rivers are the Niger and the Benue, which converge and empty into the Niger Delta. This is one of the world's largest river deltas, and the location of a large area of Central African mangroves. Nigeria has a varied landscape. The far south is defined by its tropical rainforest climate, where annual rainfall is a year. In the southeast stands the