One of the key exhibits in Maps & the 20th Century: Drawing the Line - in fact one of the key maps of the 20th century - is a world map of 1942 by MacDonald Gill. Called 'The "Time and Tide" map of the Atlantic Charter', the map was published (in Time and Tide magazine) to commemorate the signing of a wartime agreement between Britain and the United States of America in August 1941.

MacDonald Gill,  The "Time and Tide" Map of the Atlantic Charter.London, 1942. British Library Maps 950.(211.).

The treaty, which was agreed by Winston Churchill and Franklin D Roosevelt on a warship moored off Newfoundland, set out their aspirations for a post-war peace, including self-determination and global economic freedom. This symbol of friendly co-operation between Britain and the USA was designed as a threat to the Axis powers, for the USA was not at that time at war with them. The 'special relationship' dates from here.

The map brilliantly illustrates a world, unified under the sun and with images of trade and prosperity. It is a post-war Utopian vision that has been made possible by the treaty.

MacDonald Gill, ' The Atlantic Charter', 1942. Private collection.

MacDonald Gill was a highly successful British illustrator who produced work for customers as varied as London Transport, the Tea Market Expansion Board, Cable & Wireless Ltd., and St. Andrew's church, Sunderland.

He was a particularly skillful draftsman, as visitors to Drawing the Line can see from today when the original pen sketch for the Atlantic Charter replaces the printed version on display. As Gill experts Caroline Walker and Andrew Johnston have noted, Gill seems to have applied ink directly to the paper without any need for preparatory sketches or guide lines, and there isn't a smear of Tippex in sight.

Even more amazingly, the drawing has original signatures of Churchill and Roosevelt pasted onto it.

Maps & the 20th Century: Drawing the Line is open until 1 March.