Using Location Based Services To Plot Locations Of A Given Device Type
One property of MAC addresses is that they are allocated in sequence. So, if you know the MAC address of one device, you can easily derive the MAC address of similar devices.
And, once you know the MAC address of a device, courtesy of Google, you also probably know its physical location.
Here are two examples - the locations, around Sydney of up to 83 different Pocket WiFi devices that I discovered by probing a total of 256 MAC addresses.
Or, further a field, the locations around the world of 176 Apple TimeCapsule devices I discovered, once again, by probing a total of 256 MAC addresses.