How does gnome-maps get my current location?

On my desktop computer (arch) and laptop (debian) I use gnome-maps. On both devices I use a VPN. (iptables firewall does not allow non-VPN traffic, no DNS leaks.) On my desktop, the "current location" is the city where the VPN is, as expected. On my laptop however, gnome-maps is able to get my actual location (VERY precisely, almost down to the foot). How is that possible? What techniques are used? The laptop does not have GPS.