In Android Oreo (and many versions before it), the location settings screen had a Mode option on top, which unveiled three options: High accuracy (GPS + WiFi + Bluetooth + mobile networks), Battery saving (WiFi + Bluetooth + mobile networks, but no battery-sucking GPS), and Device only (GPS).But in Android P the Mode option is gone. There's no equivalent to Battery saving, so you can't turn off the GPS and rely on quasi-accurate location without sucking down your battery.
This software will add a tile at Quick Setting to switch the GPS ON/OFF.