Magnetic North and True North

A magnetic compass, including the compasses on most smart phones, does not point to the North Pole, or even to the North Magnetic Pole. Instead, it points away from True North by an angle known as the Magnetic Declination, which varies considerably, depending on where you are on the earths surface. It also varies slowly over time, as you can see in the animation on the Wikipedia page. On paper maps, this may be further complicated by a third direction known as Grid North, which refers to the direction northwards along the grid lines of the map.

We mentioned in this post a time animation for Google Earth, visualizing the Earth’s magnetic fields changing over time. You can check it out, but we had difficulty getting it to work well as an animation in the current version of Google Earth, although viewing an individual year is not a problem.

To find out what the magnetic declination in your location is, the US National Oceanic and Atmospheric Administration (NOAA), provides a handy tool on their website. There is also this useful site that lets you pick your loction on a map and tells you the magnetic declination. The ruler tool in Google Earth shows ‘heading’, so once you know your magnetic declination it is pretty easy to work out which way your compass will point in Google Earth.

Magnetic declination for Cape Town
Magnetic declination for Cape Town.

From what we can tell, the mobile versions of both Google Maps and Google Earth automatically correct for magnetic declination and always show True North, although we couldn’t find any documentation to that effect.

About Timothy Whitehead

Timothy has been using Google Earth since 2004 when it was still called Keyhole before it was renamed Google Earth in 2005 and has been a huge fan ever since. He is a programmer working for Red Wing Aerobatx and lives in Cape Town, South Africa.






PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.

Comments

  1. http://Youlanda says

    Google earth is so cool! I am from the Bahamas and is often askedquestions about the islands google earth makes it so easy to explain to my questioners & kids!!!

  2. Actually the first line is partly false. On Android devices the operating system uses your GPS location and current time to calculate the magnetic declination at your current location based on the World Magnetic Model (WMM2015). This is probably the same model used by the sites in the article. So a good android compass app is more accurate than a traditional compass.
    This is why the author believes that “the mobile versions of both Google Maps and Google Earth automatically correct for magnetic declination and always show True North, although we couldn’t find any documentation to that effect.” Any application built to use the android sensor libraries will show True North. Pretty Sweet.

    http://developer.android.com/reference/android/hardware/GeomagneticField.html

    • http://Timothy%20Whitehead says

      Thanks for the information. I had tested a compass on an iPhone and found it showed magnetic North, and Google Maps/Google Earth on an Android device and found they showed True North. I didn’t realize that it was an OS feature rather than a Google Maps/Earth feature.

      • Same is true for iOS systems. The built in iOS compass app actually allows the user to choose between true north and magnetic north. It also allows you to calibrate it to remove error caused by proximity to other magnets like in your car. Even ear buds have magnets in them. So don’t geocache while slappin a sick ditty!

  3. http://Carlos%20'Kiko'%20Campos says

    Hello, Timothy,
    Here i am asking for some help again…
    (I’m not sure if HERE is the proper place to post this question – i’m still not ‘used enough’ to GEARTHBLOG – please, let me know if i should have posted it in some other way, ok?)

    Question:

    I use to navigate using a mouse – “click & drag” way – and using the zoom with the scroll button.
    This often causes the orientation (compass) to change by itself – and i’d like it to stay pointing north ALL the time – unless I DECIDE to change it.

    Is there some setting i can use to ‘force’ Google Earth to keep on pointing north all the time, while i am navigating it? (E.G. , the way it happens in Google maps)

    Thanks again for your time and patience!

    Carlos
    from Brazil

  4. http://RobinM says

    Hello all
    I am looking for a mapping app to feed into a bespoke app, but I need it to always be set to Magnetic North. Anyone know of one ?



PLEASE NOTE: Google Earth Blog is no longer writing regular posts. As a result, we are not accepting new comments or questions about Google Earth. If you have a question, use the official Google Earth and Maps Forums or the Google Earth Community Forums.