There is no way to set the default system location, unfortunately. If you have a cable or DSL provider, at least in the US, your location will be accurate. If you're using public Wi-Fi, your location will be accurate. If you use your phone's hotspot, your location will be accurate. If you use dial-up or satellite internet, it's going to be Wonky, because your ISP doesn't provide the service properly. There may be other reasons as well.
I do wish Microsoft would allow us to set that when it's incorrect, though.
There is a way to set your default location within the weather app, and you can set a location in the maps app. Each app is specific, and some allow it and others don't. Can't help any further than that at this time.