Grid North vs True North vs Magnetic North
Three different "norths" are used in mapping and navigation: True North, Magnetic North, and Grid North. Confusing them is one of the most common sources of angular error in engineering surveys, military navigation, and directional drilling. Each has a distinct definition and a specific professional use case.
True North (Geographic North)
True North points toward the geographic North Pole — the point where Earth's rotational axis meets the surface. All meridians of longitude converge at True North. It is fixed relative to the Earth's surface and is the reference for latitude/longitude and all geodetic measurements.
- Used in: astronomical observations, geodetic surveys, legal property descriptions
- Symbol: ★ (star symbol on compass roses)
Magnetic North
Magnetic North is where a compass needle points — toward the magnetic pole in the Arctic. It does not coincide with True North and changes over time (secular variation). The angular difference between Magnetic North and True North is called magnetic declination.
- Magnetic declination varies from about -20° (west) to +20° (east) across the US
- Declination changes annually — old maps may have outdated declination values
- Source for current declination: NOAA's National Centers for Environmental Information
Grid North
Grid North points toward the top of a map grid (e.g., a UTM or State Plane grid). Because these grids are flat projections of a curved Earth, they cannot be perfectly aligned with True North everywhere. The angular difference between Grid North and True North is called meridian convergence (or grid convergence).
- On a UTM map, Grid North and True North only coincide exactly at the central meridian of each zone
- At the edges of a UTM zone, convergence can be ±3°
- In State Plane coordinates, convergence depends on the specific zone and location
Meridian Convergence — Why It Matters
Meridian convergence is the angle between Grid North and True North at a specific location. It is calculated as:
γ = (λ − λ₀) × sin(φ)
Where λ is longitude, λ₀ is the central meridian, and φ is latitude. At high latitudes (e.g., Alaska, Scandinavia), convergence grows larger and causes serious errors if ignored.
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Practical Conversion Table
| Application | Use This "North" | Notes |
|---|---|---|
| Compass navigation | Magnetic North | Apply declination correction for true bearing |
| GPS / coordinate systems | True North | All lat/long bearings are relative to True North |
| UTM / State Plane surveys | Grid North | Apply convergence correction for True North |
| Directional drilling | True North | ISCWSA standards require convergence correction |
| Military MGRS | Grid North | MGRS is based on the UTM grid |
| Legal property descriptions | True North | Metes and bounds use true bearings |
How to Calculate Grid-to-True North Conversion
- Determine your UTM zone and central meridian (e.g., Zone 17N: 81°W)
- Calculate the longitude difference: Δλ = your longitude − central meridian
- Apply: γ = Δλ × sin(φ) [in degrees, where φ = latitude]
- Positive γ = Grid North is east of True North
Convert coordinates between UTM and Lat/Long — tool includes zone information:
→ Lat/Long to UTM ConverterFAQ
Does Google Maps use Grid North or True North?
Google Maps displays a north-up orientation that approximates True North at the center of the map. Because the underlying Web Mercator projection aligns grid lines with True North at the equator, grid north and true north diverge at higher latitudes.
How large can meridian convergence get?
In UTM, convergence can reach ±3° at zone edges at moderate latitudes. At high latitudes (Alaska, Arctic regions), it can exceed 5°. In State Plane coordinates, it is typically smaller because zones are narrower.
Do I need to apply convergence correction for GIS work?
For GIS work using angular measurements (bearings, azimuths), yes. For plotting coordinates only, convergence is already accounted for in the projection math. The issue arises when mixing angular measurements from field instruments (referenced to Magnetic or True North) with grid-based coordinate systems.
What is the magnetic declination in the US?
US magnetic declination ranges from about -20° in the Pacific Northwest to +15° in Maine and the Northeast. The agonic line (zero declination) runs roughly through the eastern Midwest. Always check the NOAA NCEI Geomagnetic Calculator for current, location-specific values.
See also: Coordinate Reference Standards | Scale Factor in Surveying | UTM Anti-Collision Failure Case
US State Plane (SPCS) Converters & Local Guides
Professional engineering and surveying transformations from state-specific conformal grids to GPS WGS84.