Four lights flying in formation over the city

On Friday night, I observed four lights that appeared to fly in formation across the city, south to north. After attempting to take some photos, I began to follow the lights as best I could. After about a mile, the lights disappeared. The lights were in a 2x2 formation and stayed at the same altitude the entirety of my sighting.
 I am an aviation enthusiast and typically watch the skies. We have a regional airport in the city with small commercial aircraft, business jets, and personal aircraft. This night I had been watching some of the planes from the school circling in the pattern. Unlike those known aircraft, these lights did not have any positional strobes and were not in the pattern for the airport.
 When returned from my chase, my coworker was returning and reported seeing the same lights but he was further south when he first spotted them.