Africa 1:250,000 : Northern Nigeria.
Great Britain.War Office.General Staff.Geographical Section
[London] : War Office,
1909-12.
Relief shown by form lines and spot heights.
Initially given sheet numbering system similar to TSGS 1764, but with blocks divided into 24 sheets, numbered A to X. Later versions (from 1911) have blocks with International Map of the World numbering system, individual sheets still numbered A to X.
Graphic index in the GSGS central file.