Ghost Mode hides you from friends on Snap Map, and Snapchat documents that your location is still shared with Snap while you are in it. The location permission in your phone's settings is a different switch, and it is the one that stops Snapchat receiving your position at all.
Do they get told?Snapchat documents that the friends you pick for location sharing are not notified when you choose them. For Ghost Mode and for turning the app's location permission off, no notification is documented; Snapchat documents only that you stop being visible to anyone else on the Map. It also documents that your last position can sit on Snap Map until it expires, after 24 hours when the device permission is set to Only while using.
Do they get told?A notification to friends is not documented for Ghost Mode. What Snapchat does document: your location won't be visible to anyone else on the Map, and your own Bitmoji holds up a blue sign with a ghost icon unless you are sharing your live location. Snapchat also documents that your location is still shared with Snap.
Who can still see you
Off
Your friends on Snap Map
Your location won't be visible to anyone else on the Map for as long as the timer you pick runs.
Still on
Snapchat itself, and other apps
Snapchat documents that your location is still shared with Snap, and every other app keeps its own location permission.
Still visible
The network, and Map Snaps
Your carrier and your IP address still place the phone, and Snaps you submit to Snap Map can still show up on the Map.
Snapchat prints three timer choices — 3 hours, 24 hours, or Until Turned Off — and its own pages place the Map Settings gear both in the bottom right corner and at the top of the Map screen.
Do they get told?Snapchat documents that the friends you pick are not told: "Friends you select aren't notified when you choose them." Snapchat also documents that only friends you've chosen to share your location with can see where you're at on Snap Map.
Who can still see you
Off
The friends you leave out
They stop seeing your position on Snap Map, and Snapchat documents that the friends you select are not notified when you choose them.
Still on
The friends you keep selected
They still see your live position, and Snapchat still receives your location while the app has permission.
Still visible
The network, and Map Snaps
Your carrier and your IP still place the phone, and Snaps you submit to Snap Map can still show up there.
Snapchat prints the same choice on the Map itself: open the Map, tap the gear icon at the top of the Map screen, then tap Only These Friends or My Friends, Except…
Do they get told?A notification to friends is not documented for turning off Snapchat's location permission. What Snapchat documents is how long your last position lingers: set to Always it stays on Snap Map until you turn it off or it expires, and set to Only while using it expires after 24 hours. Snapchat also documents that your location data may still be cached after you turn permissions off.
Who can still see you
Off
Snapchat on this iPhone
Snapchat stops receiving your position from iOS, so there is nothing new for it to put on the Map.
Still on
Every other app, and iOS itself
Location Services stays on for every other app, and iOS keeps its own location for Find My and Emergency SOS.
Still visible
The network, and your last pin
Your carrier and your IP still place the phone, and Snapchat documents that your last position can sit on the Map until it expires.
Apple prints this menu as Privacy & Security, while Snapchat's own help page prints the same path with Privacy and Security and NEVER in capitals.
Location spoofing, fake-GPS apps and mock-location settings are outside this site on purpose. This page describes the settings the app and your phone provide, and what the vendor documents about them.
If someone is tracking you against your will, turning a setting off may not be the safest first step. Read this first.
Every platform this site carries for Snapchat is on the
Snapchat guide.