This map, published by George Philip in 1905, forms part of the second edition of the Philips’ Mercantile Marine Atlas. The atlas, of which this map is plate 11 of 28, was specifically intended for merchants and travellers, as a practical tool for those who operated merchant ships on international routes.

The map covers the Arabian Sea and the surrounding coastlines: the east coast of Africa as far as Zanzibar, the Arabian Peninsula, Persia, Baluchistan and India. In this section, the author highlights the main ports under British control: Zanzibar (a protectorate since 1890), Aden, Karachi, Bombay, Colombo, Madras and Calcutta. Each of the seven is accompanied by its own detailed inset at the bottom, featuring an enlarged plan of the port.

The Mercator projection is used. As this is a conformal projection, it preserves angles and allows constant-course lines (loxodromes) to be drawn between any two points. A sailor could follow these straight lines, maintaining their course with a compass, and reach their intended destination without difficulty. This, in turn, explains the network of red lines crossing the Arabian Sea from one end to the other: these are actual navigation routes connecting one port to another.

As well as the routes, the map also includes postal routes, maritime distances, telegraph cables, lighthouses, navigable channels, British and American consulates, naval stations and shipyards. Sea depths are indicated using graduated colours, information which was also essential for the safety of commercial shipping.

Sources

• The Arabian Sea