Learn whether VFR charts use true or magnetic north, how to plot a true course, apply variation and avoid common compass errors.
In aviation and real-world flying, VFR charts are geographically based on true north: longitude meridians point towards the geographic poles, and courses measured against them are true. Yet many operational details printed on the same chart, including VOR compass roses and most runway numbers, are referenced to magnetic north, so both systems appear together.
Which parts of a VFR chart use true north?
The chart’s latitude-and-longitude graticule provides the true-north reference used when plotting a course. Draw the route, then measure its angle against a nearby meridian of longitude rather than against the chart’s edge.
The top of the sheet is generally northerly, but it is not a universal measuring reference. Map projections cause meridians to converge, so a page edge or arbitrary vertical line may not point exactly towards true north at the route’s position. Our guide to reading a VFR sectional and its navigation features explains the wider chart layout.
| Chart feature | Usual reference | How it is used |
|---|---|---|
| Longitude meridians | True north | Reference for measuring a plotted true course |
| Isogonic lines | Magnetic variation | Convert between true and magnetic values |
| VOR compass rose and radials | Magnetic | Fly published VOR radials as labelled |
| Runway numbers | Normally magnetic | Approximate runway direction rounded to the nearest ten degrees |
How do you convert a VFR chart course to magnetic?
Plot and measure the true course first, apply wind correction to obtain a true heading, then apply the local magnetic variation. A practical sequence is:
- Draw the route between the departure point, checkpoints and destination.
- Measure true course against a longitude meridian near that route, using the correct scale and orientation of the plotter.
- Calculate wind correction to turn true course into true heading.
- Find the charted variation near the route. If the flight crosses substantially different variation values, calculate separate legs.
- Convert to magnetic heading: subtract easterly variation and add westerly variation. A true heading of 090° with 7° west variation becomes 097° magnetic.
- Apply compass deviation if flying from a magnetic compass and the aircraft’s deviation card calls for it.
The compact formula is magnetic = true - east variation or magnetic = true + west variation. Variation changes by place and gradually over time, so use the value associated with the chart and operational data being flown. See our explanation of how charted magnetic variation affects navigation for the underlying reason.
Why might a VOR rose disagree with local variation?
A VOR’s published radials can be based on the station’s assigned declination, which may lag behind the area’s changing magnetic variation. This can make the compass rose appear a few degrees different from a fresh true-to-magnetic calculation.
When navigating by VOR, use the published radial numbers rather than trying to correct each radial with the nearby isogonic line. In a simulator, another mismatch can arise when the chart edition, navigation database and simulator magnetic model represent different dates.
Are runway directions true or magnetic?
Runway designators normally represent magnetic direction rounded to the nearest ten degrees, which is why they do not necessarily match a course measured from the chart’s true-north grid. Long-term magnetic movement can eventually require a runway to be renumbered; our runway-numbering explanation covers the rounding and reciprocal-end rules.
There are exceptions in high-latitude regions and areas where magnetic references are unreliable. A chart may explicitly use true or grid bearings there, so check its legend and any T, M or grid-reference notation rather than assuming every value is magnetic.
Should GPS and simulator bearings use true or magnetic?
Use magnetic display mode when you want GPS bearings to agree with cockpit compasses, ATC-assigned headings, VOR radials and runway designators. True mode is valid for plotting and specialised operations, but every bearing in the workflow must use the same reference.
A common simulator mistake is comparing a GPS set to true north with an instrument or flight plan displaying magnetic headings. Before blaming scenery or navigation data, check the bearing-reference setting and distinguish course, track and heading; our guide to true and magnetic heading displays clarifies those cockpit values.