Compass vs GPS: Which Do You Need?
People often use "compass" and "GPS" interchangeably when talking about navigation. They shouldn't. They measure entirely different things — and often you need both.
What GPS Actually Does
GPS (Global Positioning System) determines your position — your latitude and longitude on the Earth's surface. It does this by triangulating signals from at least three (ideally four or more) satellites orbiting at ~20,000 km altitude. Your GPS receiver measures the tiny time differences between satellite signals and uses that to compute distance, and then position.
What GPS does not inherently do: tell you which way you're facing. A GPS receiver just knows where you are. It knows nothing about your orientation unless you're moving — in which case it can infer your heading from the direction of travel (called "course over ground" or COG).
What a Compass Does
A compass detects Earth's magnetic field and tells you your orientation — specifically, which direction is magnetic North, from which all other directions are derived. It knows nothing about your position. You could be standing in London or Lagos — the compass doesn't know or care. It just points North.
This is fundamentally different from GPS. A compass works independently of satellites, internet connectivity, or battery-intensive radios. A basic magnetic compass continues to work when your phone is in airplane mode with 1% battery — as long as the screen is on.
The Key Difference: Position vs Orientation
Think of it this way:
- GPS answers: "Where am I?" (coordinates, altitude)
- Compass answers: "Which way am I facing?" (bearing in degrees)
Modern navigation apps like Google Maps combine both: GPS tells the app where you are, and the phone's compass tells it which way you're facing so the map can orient correctly. Remove either piece and navigation degrades significantly.
When GPS Wins
- Finding a specific address: You need coordinates, not a bearing
- Turn-by-turn navigation: GPS tracks your movement and recalculates routes
- Long-distance hiking with waypoints: GPS can track your trail and mark points of interest
- Speed measurement: GPS measures velocity; a compass cannot
- Elevation tracking: Many GPS receivers include a barometric altimeter
When a Compass Wins
- No connectivity or satellite signal: Dense forests, deep valleys, and urban canyons can block GPS. A compass always works
- Stationary orientation: When you're standing still and need to know which way is North immediately — GPS can't tell you this until you move
- Low power situations: GPS is one of the most battery-hungry phone components. Compass uses far less power
- Rapid spot-checks: A compass gives you a bearing instantly; GPS takes time to acquire a satellite fix
- Religious/directional use: Qibla, Feng Shui orientation, solar panel alignment — these are compass tasks
When You Need Both
Serious backcountry navigation requires both tools used together: GPS to know your position, compass to take bearings on landmarks and cross-reference with a topo map. This combination — map, compass, GPS — is the gold standard taught in wilderness navigation courses. Each tool provides redundancy if another fails.
Phone Compasses vs GPS: Power Trade-offs
On a smartphone, the magnetometer (compass sensor) consumes roughly 0.5–1 mW of power. The GPS radio consumes 50–250 mW — potentially 100× more. In a survival situation where battery conservation matters, running a compass app instead of GPS can meaningfully extend your phone's useful life.