Does using a VPN affect GPS accuracy on a hike?

The short answer

A VPN changes how a phone's internet traffic is routed and encrypted. It has no effect on GPS accuracy, because GPS accuracy is not decided by internet traffic in the first place — it comes from the receiver chip working out a position from satellite signals, a process a VPN sits nowhere near. A route recorded with a VPN turned on should look exactly the same as one recorded without it.

Two systems that happen to share a phone

A VPN operates at the network layer: it takes traffic that would normally go straight from the phone to a website or a server, and routes it through a VPN server first, encrypted along the way. That is useful for privacy and for what a website or a network operator can see about a connection. None of it is GPS. The satellite receiver that produces a position fix does not send that calculation over the internet to be worked out somewhere else — it happens locally, inside the chip, using nothing but the timing of signals arriving from satellites in view.

This is the same separation covered in whether turning off Wi-Fi affects GPS accuracy: a network connection and a satellite fix are two different systems that happen to live in the same phone, and changing one does not touch the other. A VPN is a layer added on top of the network connection, so the same separation applies to it just as cleanly.

What a VPN could plausibly change, and why it still does not reach GPS

It is a reasonable thing to wonder about, because a VPN does change how the phone looks to the outside internet — a website checking a connection's general location by its IP address will often see the VPN server's location instead of the phone's. That kind of coarse, internet-based location guess is a completely different mechanism from GPS, built from a different data source and used for a different purpose. A recording app pulling a position from the satellite receiver never touches that IP-based guess at all, so masking it changes nothing about the track being recorded.

Where a VPN can quietly affect something — just not the track itself

The one place a VPN interacts with a hiking app at all is on the network side: uploading a route to the cloud, or checking for an update, both travel over whatever internet connection is available, VPN or not. If cloud backup happens when a phone is back online, as it does for TrailCam, an active VPN simply becomes one more hop that traffic passes through on its way — usually invisible, occasionally a little slower depending on the VPN server's location, but not something that touches the GPS points that were already recorded. The recording itself does not wait on a network connection to happen; only syncing it afterward does.

The one genuine exception, and it is not really about VPNs

A small number of apps marketed as VPNs bundle in a separate feature that fakes the location a phone reports to other apps, usually aimed at games or services that change behaviour by region. That is not something a VPN does by nature — it is an unrelated feature some VPN apps choose to add, built on iOS's developer tools for simulating a location rather than on anything about encrypting network traffic. An ordinary VPN, used for privacy or to get around network restrictions, does not do this. If a phone's reported position looks wrong in a way that has nothing to do with GPS noise — jumping to a city that was never visited, for instance — a location-spoofing feature bundled into some app is the thing to check for, not the VPN connection itself.

Things that trip people up

• Assuming a VPN could slow down or interfere with GPS the way it can slow down a web page — a VPN only touches internet traffic, and a GPS fix never travels over the internet to begin with.
• Turning a VPN off mid-hike hoping to improve tracking accuracy — there is nothing for it to improve, since the VPN was never in the path between the receiver and the satellites.
• Blaming a VPN for a route that failed to back up to the cloud — that is worth checking, since cloud sync does travel over the network a VPN is routing, but it has no bearing on the GPS track that was recorded, which is already saved on the phone either way.
• Confusing an ordinary privacy VPN with a location-spoofing feature bundled into some VPN apps — the two are unrelated, and only the second one actually changes what position an app is told.

Where TrailCam fits in

TrailCam records a route from the GPS receiver directly, the same way with a VPN running or not, since nothing about that recording depends on how internet traffic is routed. Cloud backup and sync happen over whatever connection is available once you are back online, VPN included, without changing anything about the points already recorded on the phone. TrailCam is free to download.