GPS navigation – understanding the different formats

If you travel using GPS on your bike, it is helpful if you have some understanding of navigational coordinates. Sure, in most modern GPS navigator like the Garmin ZUMO 660 you just need to enter a postcode and off you go, but drive in a foreign country, or plan a longer route at home on your PC, and navigational coordinates are suddenly very attractive to define the position of a location.

There are alternative formats to express the coordinates of a location.

The traditional nautical navigation is using degrees, minutes and seconds, and in this format, the Guildford Harley-Davidson dealership is located at 51º 12′ 18.8″ North and 0º 35′ 07.8″ West. You’ll sometimes see this format abbreviated as Dº M’ S”, I will call it “Degree Minutes Seconds”, as it is the longest format. The problem with such long formats is that its allows many places for errors and misunderstanding during communication.

Part of the coordinates can also be expressed as decimals. Here for example, the seconds are added as decimals to the minutes, and we could say that Guildford Harley-Davidson is located at 51º 12.314’N and 0º 35.131’W, or written without the special characters º and ‘, one could write:  N51 12.314 and W0 35.131.

This notation is referred to as decimal minutes, which can be abbreviated as Dº M.M’, I call it “Decimal minutes”, as it integrates the seconds information into the minutes of the coordinate.

To simplify this convention even further, we can – to shorten the coordinate to a single number – use a format that is abbreviated as D.Dº, and also called “Decimal degrees”. Here the seconds and minutes are expressed as decimal of the degree, and give the location of the dealership in just one number, as 51.20523ºN and 0.58551ºW.

Sometimes these Decimal degree coordinates are given without cardinal directions (N, S, E, and W), relying solely on positive and negative numbers instead. Using this format, anything south of the equator or west of the prime meridian is negative. So our Guildford Harley-Davidson dealership coordinates can be expressed as 51.20523 and -0.58551.

All formats have their advantages and disadvantages, some are traditionally correct but long, other are easy to use in spreadsheets but are not as intuitive. The very short decimal degree is often used as geotag pictures  in photo cameras.

I learned my navigation decades ago to sail the oceans on a sailing yacht, and am quite familiar with the nautical “Degree Minutes Seconds” format. But it is quite a long format, and in these modern times – and on this blog – I will use as helpful compromise the “Decimal minutes” notation, with cardinal directions, although I doubt my Road King will ever venture south of the equator.

The “Decimal minutes” notation uses less numbers and only 1 space, but the minutes are still recognizable and just the seconds are broken down into decimals. I like to know that I live 22 minutes (and a bit) north of the 51 degree north. The “Decimal degrees” notation is for me a step to far away from tradition and the roots of navigation, and it does not sound very exciting that I live at 52.20511.

So, for this blog, and other posts,  the HD bling shop in Guildford is at N51 12.314 and W0 35.131, and using Google this string will return a accurate result on a map and satellite picture:

The good news is that you should never have to manually convert from one format to the other, your GPS and most software programs (like Google) will do it for you.

But be careful to enter the correct format, with all spaces. So please remember:

  • N51 12.314 and W0 35.131 is the Decimal minutes format, my preference and
  • N51.20523 and W0.58551 is the same address expressed in Decimal degrees

Again: be careful, if you omit some space or move the decimal point, thus entering Decimal minutes data in a Decimal degrees format, like N51.12314 and W0.35131, you end up 15 miles away, still in Surrey, but now near Ockley, and trust me, there is no Harley Davidson dealership there.

Here again in summary the different formats of location for the Guildford Harley-Davidson dealership.

If you pay attention to the spaces and decimal points to recognize the format, you and your GPS will always find your destination.

Have a safe drive

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5 Responses to “GPS navigation – understanding the different formats”

  1. Hey There. I found your blog using msn. That is a really neatly written article.
    I will make sure to bookmark it and come back to read extra of your useful info.
    Thank you for the post. I’ll certainly return.

  2. Very good article. Thanks!.
    I have also noted that some sources also manage the GPS in a Long number format, which its a bit less precise. Have you seen this format in place?. How to convert to it?.

    • Yes, the decimal only format is mainly used in electronic devises like iPhone and GPS enabled cameras. Not sure how to convert, but could well work just entering it in Google Maps

  3. prometheus Says:

    Thanks a lot. Very good explanation. 🙂

  4. Charles Smith Says:

    Thanks for that – very clear!

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