The van Keulen family publishing house in Amsterdam was founded in the late 1670s and continued production into the early 19th century. Johannes van Keulen I, the originator of the business (1654-1715), his son Gerard (1678-1727), and his grandson Johannes II (1704-55) produced high-quality sea atlases covering the oceans and seas of the world, including editions of their Zee-Atlas in Dutch, English, French and Spanish. By the mid-18th century they also produced some more localised charts, of which this is one example by Johannes van Keulen II, thought to have been produced initially around 1756. It is cleverly designed, through the use of two separate charts at different scales, to deal with the geographical intricacies of the outer approaches to the Firth of Clyde and of the inner reaches leading in to Glasgow.
The smaller-scale chart shows the approaches via the North Channel into the Firth of Clyde, and navigating the narrows between the north coast of Ireland and the Mull of Kintyre. The larger-scale chart illustrates the route up the Firth of Clyde from between the islands of Bute and Great Cumbrae, and then through the channels in the inner reaches of the Clyde past the Clyde ports of Gourock, Greenock and Port Glasgow. Safe anchorages are shown with an anchor sign, and depths of water are also given.