SIEM REAP, CAMBODIA — For decades, archaeologists here kept their eyes on the ground as they tramped through thick jungle, rice paddies and buffalo grazing fields, emerald green and soft with mud during the monsoon season.

They spent entire careers trying to spot mounds or depressions in the earth that would allow them to map even small parts of Angkor, the urban center at the heart of the Khmer empire, which covered a vast region of what is now Cambodia, Thailand, Vietnam and Laos from roughly A.D. 802 to 1431. In modern times, little material evidence existed beyond a network of monumental stone temples, including the famed Angkor Wat, and the sprawling settlements that presumably fanned out around the temples long since swallowed up by the jungle.

But earlier this year, the archaeologists Shaun Mackey and Kong Leaksmy were armed with a portable GPS device containing data from an aerial survey of the area that is changing the way Angkor is studied. The device led them straight to a field littered with clods of earth and shot through with tractor marks. It looked to the naked eye like an ordinary patch of dirt, but the aerial data had identified it as a site of interest, a mounded embankment where the ancestors of today’s Cambodians might have altered the landscape to build homes.