Ancient & Renaissance Cartography

Around 240 BCE, Eratosthenes, chief librarian at the Library of Alexandria, learned that at noon on the summer solstice, the sun shone directly down a well in Syene (modern Aswan), casting no shadow at all. On the same day in Alexandria, he measured the shadow angle of a vertical stick and found it to be roughly 7.2 degrees — about one-fiftieth of a full circle. Knowing the approximate distance between the two cities, he multiplied it by fifty and arrived at a figure for the Earth's circumference that lands remarkably close to the modern measurement of roughly 40,075 kilometres, depending on which ancient unit of distance he was actually using.

This wasn't a lucky guess — it was a genuine application of geometric reasoning to a planetary-scale problem, achieved with instruments no more sophisticated than a stick and a well.

Around 150 CE, the Alexandrian scholar Claudius Ptolemy compiled the Geographia, cataloguing coordinates — latitude and longitude — for roughly 8,000 locations across the known world, and, critically, introducing systematic methods for projecting a curved Earth onto a flat map. Ptolemy's own coordinate errors were often substantial (he significantly underestimated the Earth's true circumference, a mistake later inherited by Columbus's own calculations), but his underlying mathematical framework — that location could be captured through a coordinate system and translated through defined projections — became the conceptual foundation cartography still rests on.

In 1587, a Milanese nobleman named Urbano Monte — a gentleman scholar rather than a professional cartographer, who researched from libraries rather than voyages — completed the largest known world map of the early modern era: sixty hand-drawn manuscript sheets, meant to be pasted onto a ten-foot wooden panel and rotated on a central pin driven through the North Pole. He specified the assembly instructions himself in the map's dedication. For over four hundred years, no one actually built it. The sheets survived instead bound flat inside an atlas, their true scale invisible.

That changed in 2017, when the David Rumsey Map Center at Stanford acquired one of only two surviving manuscript copies and digitally stitched all sixty sheets together for the first time — finally revealing Monte's map exactly as he had conceived it: a single vast circular planisphere over three metres across.

The map uses an azimuthal equidistant projection centred on the North Pole — every point plotted at its true proportional distance from that centre — a genuinely advanced choice for 1587 that would not become common in mapmaking for another three centuries. Monte's ambitions went beyond geography: the planisphere layers in regional climate, local customs, and length-of-day data, an attempt at what its cataloguers call a "universal scientific planisphere" rather than a simple coastline chart.

It is also, unmistakably, a document of its time. Alongside genuinely researched detail — his depiction of Japan is unusually accurate, likely informed by the Japanese embassy that visited Milan in 1585, an encounter that appears to have sparked his interest in cartography in the first place — the map is scattered with mermaids, unicorns, and other imagined creatures in the unmapped corners of the world. Science and fantasy sit side by side without any apparent tension between them.

Every subsequent debate about map projections — including the modern reckoning with Mercator's own distortions, covered elsewhere in this collection — inherits its basic vocabulary and mathematical framing directly from this period. Eratosthenes proved the planet could be measured; Ptolemy proved location could be systematically coordinated and projected. Everything since has been refinement of that basic premise, not a departure from it.