This Key, or index, sheet to Popple's 'Map of the British Empire in America', is a faithful and accurate reduction of Popple's wall map, including the title and dedicatory cartouches, all vignettes, and even Edmund Halley's endorsement. However, its smaller size necessitated fewer topographical details, and in that respect, it is very similar to a surviving manuscript map in Popple's hand (see Pritchard and Taliaferro). In addition, this Key map bears gridlines and numbers to show how to assemble the larger map.

When it was published in 1733, Popple's wall map was one of the two most important maps of North America published in the eighteenth century on a grand scale: along with John Mitchell's 'Map of the British & French Dominions in North America', Popple's map was a profound statement of England's designs for dominance of the North American continent, at a time when colonial control of North America was by no means certain. The first large scale printed map to show, and name, the 13 British colonies, it was nearly eight feet square when joined, and showed the extent, not just of the British, but also the French, and Spanish colonial possessions of North and Central America, and the West Indies.

"Little is known of Henry Popple, except that he came from a family whose members had served the Board of Trade and Plantations for three generations, a connection that must have been a factor in his undertaking the map, his only known cartographic work" (McCorkle). His father and grandfather both served as secretary to the board. When his father resigned, Henry's brother, Alured, inherited the post. Henry was offered a clerkship in 1727. "Finding that position unprofitable, he resigned to work as a private financial agent for the West Indian governors and some British regiments. In that capacity he appeared before the commissioners on numerous occasions" (Pritchard & Taliaferro). Alured eventually accepted the post of governor of Bermuda, in which post he was succeeded by another brother, William.

As with the larger map, the Key sheet was engraved by William Henry Toms. The elaborate title-cartouche is a beautifully executed miniature of the original by Bernard Baron. However, Popple credits the design of the larger map to the Channel Islander Clement Lempriere, a military cartographer attached to the Corps of Engineers and later Chief Draftsman at the Tower of London, who subsequently worked on other projects with Toms.

Despite the evident need for a map such as Popple's, and his connection to the Board of Trade and Plantations, it was not initially a commercial success. Publication of the map was taken over by William Henry Toms and Samuel Harding in August of 1739, at the outbreak of the War of Jenkin's Ear, when it eventually found its commercial moment and sales soared. They advertised it frequently in the newspapers, with their last advertisement appearing in July 1745. In 1746, the rights to Popple's map were sold to Willdey and Austen, who published the map until Austen's death in 1750 (Babinski, Notes 4-8). This is Babinski's state 4, showing the track of the Spanish Galleons.