From an altitude of 17,500 feet a drone with a 1.8 gigapixel video camera can monitor half of Manhattan.
The interface shows the wide field of view all at once but 65 windows can be opened up showing zoom in views of different spots. They can see things as small as 6 inches like birds. They can make out people waving from the ground and what they are wearing.
The software analyzes and tracks everything that is moving.
All of the images is archived from every UAV. The persistent monitoring means that any past time can be selected for a monitored area and what happened at that time can be played as if you were watching it live.
The sensor uses four lenses and 368 cell phone cameras, 5 megapixels each.
Each chip is receiving the light from one tube. The video below does not reveal what the system looks like, but I am pretty sure it looks like the system shown in a patent from 2007.
The ARGUS-IS, or the Autonomous Real-Time Ground Ubiquitous Surveillance Imaging System, is a Defense Advanced Research Projects Agency (DARPA) project contracted to BAE Systems. Nextbigfuture covered this system in 2009.
Another DARPA project should have developed a 50 gigapixel camera out of off the shelf parts. Mass production could bring the cost of 50 gigapixel systems down to about $1000. 50 gigapixels would mean increasing resolution to make out 1 inch objects from 17500 feet or viewing a larger area at the 6 inch resolution.