Surveillance is a major aspect in the kingdom Nimona takes place in. The law enforcement of the kingdom, the Knights, have access to surveillance cameras posted all across the Kingdom. Midway into the movie, we see a massive room of workers dedicated to scanning these video feeds with facial recognition software in pursuit of Nimona and Ballister. Infrastructure and usage like this doesn't suddenly pop up when a major enemy of the state is being pursued, and its clear that this is something which the Kingdom has been using for some length of time at the point in time in which the plot takes place.
This scene in Nimona features the camera room connected to surveillence cameras ran all throughout the Kingdom, which successfully locate the two people out of an entire city which they are attempting to locate.