Database of the region's 4G cell towers: a phone connected to a tower identifies it by the network (MCC + MNC, often shown together as the « PLMN ») and the station ID (eNB). The tool gives the mast's location and the direction of its sectors.
Reading a « network info » screen
PLMN = MCC (3 digits, 208 for France) + MNC (the operator). In 4G, the cell ID ECI (28 bits) combines the station and the sector: ECI = eNB × 256 + sector. Divide the ECI by 256: the whole part is the eNB, the remainder the sector number.
In real life: CellMapper, OpenCelliD, Cartoradio (France's ANFR) for official tower locations. Rescuers and investigators use them to estimate a search area: a sector covers an angle of about 120° around its azimuth.