After the reign of the Khmer Rouge ended, Angkor was not yet ready for exploration as the last groups of the Khmer Rouge with their leader Pol Pot made their last stand in the Kulen Hills. Only after the death of Pol Pot that it became safe for exploring, archaeologists started returning to Angkor to once again explore the Khmer history.
The one advantage of this was that by this time, new technologies had emerged which would make exploration of the area a lot faster and easier. NASA had developed ground-sensing radar in 1960s and this was brought into play for exploring Angkor only in 2007. This technology was particularly conducted by helicopters flying above Angkor. With this immense technology in hand, the archaeologists figured out that Angkor was not just something big, it was an extensive city as big as any modern day metropolis.
At the epicentre of this city was the temple of Angkor Wat and closer to that, the fortified area of Angkor Thom. The city was spread out far and wide. Well, when you think of such an extensive area, it would require all the necessities to support the booming population of that city. The most important in this region was water, Cambodia was and still is a monsoon-dependent country for water. Even other economic activities, mainly cultivation of rice were governed by this.