Last year a Cessna (a Skylane or Stationair) orbited the around central SF for several hours over 3 or 4 days. The edge of the track was right over my block. It would drone by every few minutes. It did not have a removed door or anything that would indicate camera platform. The constant orbit wouldn't make sense as an photographic mapping platform.

It was not on flighttrack, no ADS-B info, and too high to see the N number.