The ancient world's understanding of geography shaped its understanding of history in ways that are sometimes startling to modern readers accustomed to accurate maps. The oikoumene — the 'inhabited world' — was bounded by the ocean, and peoples at the edges of the known world were expected to be increasingly strange.

Herodotus' ethnographic methodology — describing the customs and geography of peoples as far as his sources could reach — was shaped by the assumption that distance from the center (Greece, or later Rome) correlated with difference. The further you traveled, the more different the people: gold-guarding griffins in the north, people with no heads and eyes in their chests (Blemmyae) in Africa, dog-headed people in India. These were not simple credulity but the application of a principle that the center was normal and the periphery bizarre.

The Roman imperial sense of geography was shaped by its administrative needs: the road network, the military frontier, the provincial tax system. Ptolemy's Geography (2nd century AD) attempted a systematic mathematical geography using coordinates, but the projection methods were imperfect and the data for distant regions was unreliable. The distortions in Roman maps of Britain (too wide), Scandinavia (barely present), and sub-Saharan Africa reflect the limits of Roman geographic knowledge.

The relationship between geographic knowledge and imperial ambition was direct. Caesar's invasion of Britain was explicitly presented as extending Roman rule to the furthest edges of the world; Augustus' map of the empire (the Orbis Terrarum displayed in the Porticus Vipsaniae) was a visual statement about the coincidence of Roman rule with the inhabited world. Geographic knowledge was political knowledge.