Deja Vu stores the locations of wifi APs and cell towers on your phone. This allows for greater accuracy than using gps alone and allows you to do it without pinging google may times a day like stock android phones with location services turned on do.
This app requires MicroG’s UnifiedNlp to work which requires a ROM with signature spoofing enabled. The easiest way to get this is to use a custom ROM like Lineage with Microg or use NanoDroid with a custom ROM.
Important app for retaining functionality while degoogling your android phone.