I resolve the familiar exploring the same way I would a (flying, if the familiar can fly) PC exploring. The player describes where the familiar goes and what they do, and I describe what it can perceive while doing so. If the players want to make a map from that they can, but it’s not automatic, and the familiar has to search for hidden features the same way a PC would. If your players are expecting to be able to skip those processes and just have you tell them every detail of the map automatically, I can certainly see that being annoying. But I would think a simple “that’s not how the spell works, the familiar has to actually explore and experience the environment through its direct senses” would resolve the issue.