From the hieroglyphs of Aztec Mexico to the red stripe of London's Central line, all maps are idealised representations of the world. A relief map of moorland fells can mesmerise with its geometric language of lines and symbols. Yet even with the world now so thoroughly mapped out by Google, many of us remain carto-illiterate. In the mid-1990s, drivers in Britain were wasting an extraordinary 80m gallons of petrol each year getting lost, according to the AA (one would hope that figure is lower now, thanks to satnav). Those of us with poor visual-spatial skills often find it easier to read road atlases upside down.

Maps of all kinds permit a greater understanding of history and the politics of cartography. Nazi map-makers redrew Europe's frontiers in the shadow of the swastika, with an emphasis on "Jew-free" (Judenfrei) areas of conquest. The first surveys of the Scottish Highlands were done to facilitate the crushing of rebel clans in the wake of the Jacobite uprising of 1745. In spite of their political intent, the maps provided a magnificent bird's-eye view of mid-18th-century Scotland. The bunched contour lines and triangulation points marked on modern-day Ordnance Survey maps would not have been possible without the earlier charting of Scotland. In this endlessly absorbing history, Rachel Hewitt narrates the history of our printed maps from King George II's "Scotophobic" cartographies to the three-dimensional computerised elevations of today. A marvel of exactitude and the quantifying imagination, the Ordnance project conjures a "Betjemanesque image" of cycle-touring and jolly tramps through bog and heather. Founded in 1791 as the Trigonometrical Survey, it nevertheless began life as a military venture, merciless to subject peoples.

Herself a keen hiker, Hewitt portrays a heroic enterprise assailed on all sides by professional vanities, lack of funds and other difficulties. In post-Culloden Scotland the map-makers had used a small, tripod-mounted telescope or prototype theodolite to measure sight-lines from landmark to landmark. Inevitably, their arrival in a land pacified by a foreign power aroused fears of continued surveillance. Half a century later, when the first Ordnance Survey map was released to the general public in 1801, the project was still viewed with suspicion. In intricate black-and-white the map revealed Britain's south-easterly corner as a mesh of bridleways, brooks and field boundaries. Few could have guessed at the difficulties involved. As the surveyors scanned the Kent horizon with their telescopes, locals had mistaken them for French spies.

Notoriously, in 1824 government map-makers moved to Ireland. Their presence provoked such levels of suspicion that it seemed the entire British judiciary, church and crown were under threat. The Irish Ordnance Survey became the subject of Brian Friel's play Translations; it remains an incendiary moment in Irish history.

The Irish were not the only people to see maps as instruments of intimidation and control. Hewitt charts the hostility shown to "engineer agents" by Romantic poets and writers. William Wordsworth, for all his avowed interest in the Ordnance project, was critical of those seeking to tame the countryside by means of their boxed precision instruments. The Board of Ordnance may share the enlightened conviction that the pursuit of knowledge was a sovereign good, but they preached a godless, functional clarity. For William Blake, the "ésprit géométrique" that defined the national survey project was nothing short of satanic. Why enslave the human mind to universal laws and the cold hand of rationality?

Triumphantly, the Ordnance Survey has swelled over the years into a cartographical institution that comprises 403 maps in the Explorer series of the British Isles. Each region, no matter how inaccessible, possesses its own "biography" of streams, pre-Christian earth mounds, coach stations and lay-bys. In her lively and informative narrative, Hewitt highlights the Ordnance project's legion of draughtsmen, surveyors, dreamers and eccentrics, and the disagreements that flared among them. Prior to the 18th century, Britain of course had its national maps, but, emblazoned with royalist insignia or overtly patriotic, their function was primarily symbolic. The entire nation is now mapped out in exact and unbiased detail. Something may have been lost by charting every last footpath, boulder and scree slope, but we have become more "map-minded" as a result.

Ian Thomson's The Dead Yard: Tales of Modern Jamaica won the Royal Society of Literature Ondaatje prize 2010

The "cubist jigsaw of overlapping sheets" that is the Ordnance Survey of Great Britain is a national treasure, cherished by ramblers and right-to-roamers, but in Map of a Nation Rachel Hewitt reminds us that its origins are military and that it is, in fact, part of "a long history of British military efforts to subdue neighbouring territories through cartography".

The OS began with the idea of a "military survey of Scotland", which would facilitate the occupation of the Scottish Highlands. Redcoats trying to root out Jacobite rebels in the most inaccessible Highland regions were hampered by inaccurate intelligence. "This place is not marked on any of our maps," Captain Frederick Scott objected in a letter to his commander in 1746, a month after the battle of Culloden. The rugged landscape was, quite literally, "unreadable" and the rebels were getting away.

Employed by the Board of Ordnance, William Roy began mapping the Highlands in 1747, pushing a surveyor's wheel and using a simple kind of theodolite called a circumferentor. Later he was joined by a "ragtag bunch of young surveyors" and they finished mapping the entire Scottish mainland in 1755. The Military Survey of Scotland, drawn in pen and ink with watercolour washes, offered "a vast, gorgeous bird's-eye view of mid 18th-century Scotland". But Roy didn't stop there. His dream was a complete map of Britain.

The French had begun their own mapping project more than a century before, and the Carte de France (1756), a complete national map of unprecedented accuracy and scope, was a model for the OS. It was, Hewitt argues, "the highest ideal of the Enlightenment: perfect measurement of the ground beneath our feet". However, war with France changed all that. The survey, begun in 1791, quickly became part of Britain's defence strategy, as England's south coast and the far south-west corner of Wales were mapped to assess their vulnerability to French invasion.

Before it had finished mapping England and Wales, however, the OS turned its attentions to Ireland. The Irish Ordnance Survey, begun in 1825, is easily caricatured as a "tool of English imperialism", Hewitt says, but in fact it was an attempt by Irish-speaking Catholics to salvage Ireland's ancient cultural heritage. Place names were always "a mighty headache to early mapmakers". Some surveyors wrote down the first name they heard; others were more conscientious. Some of the mistakes are worthy of Finnegans Wake: the ancient name of Queen Taillteann, for instance, was transcribed by one mapmaker as Telltown, while Monaster O'Lynn (O'Lynn's Monastery) became "Moneysterlin".

This is a solid account of how Britain's national mapping agency came into being, though it lacks a certain pizzazz. Hewitt works hard to bring the story to life, but it is perhaps inherently undramatic. Nevertheless, she is good on the military, scientific and ideological impulses behind the OS and on its enormous appeal to the general public. The first map (Kent and part of Essex) was made available in 1801 and not long afterwards surveyors were being pestered by tourists in search of the sublime or picturesque. One director of the Ordnance Survey objected to these "swarms of idle holiday visitors" and fantasised about working in "almost inaccessible positions", free from "disagreeable intrusions". Paradoxically, the very men who had opened up the landscape to the people still dreamed of getting far from the madding crowd.