A Victorian map-maker at work in Ireland was asked what he was doing, writes Hewitt. To explain his purpose, he first had to inquire: “Do you know what a map is?” and carefully explain that it was “a representation of the land on paper”.

It will be a sad day if the SatNav generation succeeds in sending the Ordnance Survey map into a forgotten landscape of slide rules and logarithm tables, milk vans and post offices, paper books and friendly lollipop ladies.

Like a good book, a good map sends a tingle down the spine of country lovers, and those of us who have struggled with French and Italian maps have cause to salute the stalwart work of the Ordnance Survey.

It’s interesting that the second choice of many keen walkers would be a German map. Maps have their origins in the military, and the Empire builders of Britain were first stirred into action by the rebellion fomenting over the Scottish border after Bonnie Prince Charlie’s 1745 uprising, with the rebels able to disappear into the unmapped Highlands.

Hewitt compares the map-makers to the compilers of the Oxford English Dictionary. Both projects were immensely expensive, and took generations to create. They are monuments to the mammoth aspirations of the Victorian age.

She describes how the astrolabe, the plane table and the theodolite conquered the unmapped Scottish mountains, with the map-makers devoured by midges, sweating in woollen uniforms as they trudged over the wilderness of desolate bog and moorland.

At that time the French were ahead in the map-making game, and they joined the Royal Society in fixing the longitude and latitude of the Paris and Greenwich observatories.

The book presents an engaging account of the troubled path towards France and England becoming ‘trigonometrically bonded’. It was a shortlived interval of co-operation, and soon William Mudge was drawing up a detailed map of Kent to counter the threat of invasion by Napoleon.

Hewitt ends her very scholarly history in 1870, but permits herself a final chapter on the “seductive” promise of maps, including the beautiful picture above of 1930s hikers claiming the new freedom to explore the countryside.

Obviously an experienced hill walker, she is optimistic about the future, saying: “Ordnance Survey maps never had the monopoly on geographical information”, and revelling in the multiple sources of information we now enjoy.

* Rachel Hewitt will speak at the Oxford Literary Festival on April 5. See www.oxfordliteraryfestival.com.