Factual error: When requesting images from the satellite, the position (latitude and longitude) is always given in degrees and minutes (but NOT seconds), and a few moments later they get a picture centered on the person they are looking for. Now a minute equals a nautical mile (or 1.85 kilometers), so with a position given in degrees and minutes you'd get a region bigger than 3 square kilometers.... which makes it impossible to find a person that fast (especially in a crowded town).
Factual error: While escaping from thugs in Hackman's pickup, Smith points a sawed-off shotgun in front Hackman's face and fires at the baddies. Hackman should have been deaf, but he didn't even blink.
Factual error: Satellite images only work on clear days with no clouds. But most of the days shown in the movie are cloudy which would make most of the spying impossible.
Factual error: After Will Smith escapes the ambulance and runs into the transit tunnel, NSA crew tunes to the frequency 7.210 Mhz as indicated by a piece of tape stating that is the City authority frequency. Trouble is twofold. First that frequency is an Amateur Radio (Ham Radio) frequency, only for use by licensed amateurs, and second all municipalities and local organizations use VHF frequencies and higher due to propagation and the antenna lengths involved in order to talk to mobiles and vehicles. The frequency should have been above 150 Mhz to be accurate.
Factual error: When the NSA people identify Brill and go through his file, they tell us that he graduated from Drexel University in 1964. Brill could not have graduated from Drexel University (DU) in 1964 because it was called Drexel Institute of Technology (DIT) at that time, which is the name that would be in the official file. It didn't change from DIT to DU until 1970.