Maps do more than show us where we are or help us find where we need to go. They are powerful cultural documents, reflecting – and often shaping – the values, priorities and secrets of the societies that create them.

This lesson is brought to vivid and sometimes unsettling life in the British Library’s new exhibition, Secret Maps, which draws on more than 100 remarkable items to trace the long and tangled history of mapping as a tool for both revelation and concealment.

From hand-drawn naval charts presented to Henry VIII, to the satellite data hoovered up by our smartphones, the exhibition explores how, across centuries, maps have given form to power, plotted imperial ambitions, and encoded anxieties about security and privacy. But it also shines a light on how maps have empowered communities, memorialised injustice and contested official narratives.

One of the most striking themes of Secret Maps is the use of cartography as an instrument of state secrecy. Many of the earliest items on display were never meant for public eyes: confidential maps of the English coast commissioned for Tudor monarchs, closely guarded charts of “secret” trading routes by the Dutch East India Company and classified military plans for the D-Day landings. The shaping of knowledge was, and often still is, an act of geopolitical strategy.

A particularly evocative display pairs an 1876 map of Dover stripped of its military details for public consumption with a “secret” version, replete with every........

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