Does turning off Wi-Fi affect GPS accuracy on a hike?

The short answer

No, not in any way that matters once a recording is running. Position comes from timing radio signals broadcast by GPS satellites, a process the receiver chip carries out entirely on its own. Whether Wi-Fi is on or off does not change what that chip can see in the sky, and Wi-Fi has no part in computing any of the points that end up on a recorded track.

What Wi-Fi and cellular data actually do is help the very first fix arrive a little faster, in places where a network happens to be reachable. That is a genuine, if minor, convenience at the start of a walk. It is a different claim from "GPS needs Wi-Fi to work", and once a route is a few minutes old it stops applying at all.

What a network connection actually speeds up

A phone's location system is built from more than the raw satellite receiver. When a network is reachable, it can also reach for two shortcuts. The first is a rough starting estimate, worked out from which Wi-Fi access points and cell towers are nearby, since the approximate location of known ones is already on file. The second is the satellite orbit data the receiver needs before it can turn raw signals into a position — data that can arrive over a network in a couple of seconds, instead of waiting to pick it up directly from the satellites, which takes longer.

Both shortcuts only affect how quickly the first fix arrives. Neither is used to compute the position itself once a proper fix is established — that number always comes from the satellites, network present or not. This is the same distinction covered in why GPS takes a few minutes to settle at the start of a hike: a cold start is slower without help. It is not less accurate once it resolves.

Why it rarely matters on an actual trail

The shortcuts above only help if there is a network to reach in the first place, and most of a hike takes place somewhere that is not true. A trailhead car park might sit in range of a cell tower or a nearby house's Wi-Fi; a ridge two hours in almost never does. Once nothing is reachable, leaving Wi-Fi on or off stops being a meaningful choice, because there is nothing for it to connect to either way — the phone falls back to working everything out from the sky alone, which is exactly what it does with Wi-Fi off from the start.

This is the same situation covered in tracking a hike without cell service: a GPS fix and a network connection are two separate systems that happen to share a phone, and only one of them needs anything overhead beyond open sky.

Where switching Wi-Fi off does help

Battery, in a small way. A phone with Wi-Fi on periodically scans for nearby networks even when it is not connected to one, and that scanning costs a little power for no benefit if nothing is ever in range. It is the same category of waste as a cellular radio searching for a tower it cannot reach, covered in GPS battery drain on iPhone, just smaller in practice, because scanning for Wi-Fi is a lighter operation than a cellular radio hunting at full power.

Airplane mode is the setting that actually matters here on a day spent out of coverage, since it stops the cellular search outright. On an iPhone, Wi-Fi can be switched back on without leaving airplane mode, so cellular search stays off while a specific network, if one happens to be reachable, is not. Location keeps working through all of it, because none of it touches the satellite receiver.

What TrailCam does

TrailCam records a route from GPS in the background and does not need a data connection to do it — the same recording that works with no signal at all works exactly the same way with Wi-Fi switched off. Distance, moving time, pace and elevation gain are all worked out afterward from the points the receiver actually logged along the way. It is free to download.