THE SURVEY FRAMEWORK OF NIGERIA
John Wood · Empire Survey Review · 1937
The vertical framework of Nigeria comprises a network of primary instrumental levels and trigonometrical heights. The primary levels consist at present of (1) a network in the South-western Provinces, (2) a continuous line of levels from Lagos through Ibadan, Ilesha, Akure, Benin, Onitsha, Awka, Okigwi, Aba, and Port Harcourt to Bende in Calabar Province, and (3) a further line from Ilesha to Oshogbo and thence along the railway to Minna, where it is connected to L41, the south terminal of the Minna base. The total mileage of double levelling is 1,128 miles. Trigonometrical heights have been determined by reciprocal observations over all the primary chains.