Is WiGLE a thing people know about? How does that work, its a service that listens to all publicly available wifis in the country? I understand how it could be possible in theory but how is it actually practical?
Data is crowdsourced and contributed by users. On a much larger scale, Apple and Google collect data from iOS and Android devices to power their WiFi/mobile tower based geolocation services.
Mozilla also has such a service although I believe they're deprecating it. You can still query it today, but as a privacy measure you need to include the MAC of 3+ SSIDs to get location info, since otherwise you could check the SSIDs from probe scans of passerby to locate their homes.
Wigle is not a thing that people know about. It isn't a secret (at all) -- in fact, it was created in part to raise awareness about the problems associated with open-by-default consumer wireless routers.
But, like (say) RIPE Atlas, it just isn't very commonly known.
Data in Wigle is collected mostly by wardriving, which (in a nutshell) is just driving around and passively recording the information that WiFi access points are shouting about themselves to whoever is listening.
The data is collected by volunteers, but it is not strictly free. The way that the project is funded is by selling the data to companies who use it for geolocation services.
Regular folks can do some basic searches on the dataset without cost, though, which is what the author has done here.
Android's Location Services: https://support.google.com/android/answer/3467281#location_a...
iOS's Location Services: https://support.apple.com/en-gb/102515
In fact, Google provides it as a paid API: https://developers.google.com/maps/documentation/geolocation..., but you require BSSID's and not just SSID names to try to curb abuse.