Even with all of our modern aviation databases, sometimes you just can’t beat a lat/lon coordinate. Maybe you’re visiting a private airport that isn’t in the database, or you want to circle a landmark not on the sectional, or you need to plan a flight around a TFR. Whatever the reason, entering a set of coordinates in your favorite app is easy. But there are a couple of traps you need to avoid, and not everyone reports lat/lon the same way. Let’s review the basics of latitude and longitude and the different types of coordinates.
Latitude and longitude have been in use for almost 2000 years, and they’ve stood the test of time because the system is both simple and powerful. Any point on Earth can be described with a few numbers, making lat/lon coordinates the backbone of all GPS navigators and mapping applications. Lines of latitude measure north-south position, with the equator at 0 degrees and the North Pole at 90 degrees North. Lines of longitude measure east-west position, with 0 degrees at Greenwich, England.
When it comes to expressing more specific locations, things get more complicated. There are three main ways to describe a lat/lon coordinate:
- Degrees, minutes and seconds (39° 4′ 47.9″ N / 84° 12′ 35.9″ W). This is the traditional format for lat/lon, used for years on paper maps. But it’s pretty difficult to do much math with this format, so newer formats are increasingly popular (see 2 and 3 below).
- Degrees and decimal minutes (39° 4.8 / -84° 12.6). Instead of seconds, this format uses minutes with a decimal point, and is most often used with electronic navigation equipment. For example, if you create a new user waypoint on a Garmin hand-held GPS, the location will be stored in this format. Note that the -84° signifies West; +84° would be East.
- Degree decimal (39.08, -84.21). This is increasingly common, and is preferred by most computer sources – including Google Maps. Again, the – sign is used for West and South, so you would enter 39.08,-84.21 in Google for the Clermont County Airport in Ohio (I69). This is also the format used in most aviation apps, although as we’ll show below, other formats are also accepted.
The problem we’ve run into is when you mix sources. Say you find the perfect grass strip on Google Earth and copy the coordinates (in degree decimal format). If you then put that in your Garmin GTN 750 (which uses degrees and decimal minutes), it will be off by a good margin. The trick is to know what format each source uses – website, GPS and iPad – and convert if necessary.
The good news is that the iPad makes it at least a little bit easier. For example, ForeFlight can accept lat/lon coordinates in either the route editor or the search box on the Maps tab.
All three formats are supported, with either the N/S/E/W or the +/- symbols. Also note that ForeFlight uses / to separate the coordinates, not a comma as you’ll find online:
- Degrees, minutes and seconds with N/S/E/W (enter N324455/W0804557 for the coordinate 32°44’55”N, 80°45’57”W).
- Degrees, minutes and seconds with +/- sign (324455/-0804557 for 32°44’55”N, 80°45’57”W)
- Degrees, minutes and seconds with extra decimal point, using +/- sign (3244556/-08045576 for 32°44’55.6”N, 80°45’57.6”W). Note that in all three of these examples where we use degrees, minutes and seconds, a 0 is required before the 804557; entering -804557 will not work. For the examples below, you may omit the 0.
- Degrees and decimal minutes with N/S/E/W (3244.92N/8045.95W for 32°44’55”N, 80°45’57”W)
- Degrees and decimal minutes with +/- sign (3244.92/-8045.95 for 32°44’55”N, 80°45’57”W)
- Degree decimal with N/S/E/W (32.7N/80.8W for 32°44’55”N, 80°45’57”W)
- Degree decimal with +/- sign (32.7/-80.8 for 32°44’55”N, 80°45’57”W)
If you tap and hold on the Maps page, or if you use the Marked Position feature, ForeFlight will default to degrees and decimal minutes (39° 4.8N/84° 12.6W is how it appears in the pop-up window).
In Garmin Pilot, you can enter a lat/lon coordinate on the Active Flight Plan or the Trip Planning pages. The app will accept all three formats, but you must choose which type you prefer from the Settings menu -> Units page. You can also change the format directly from the Create User Waypoint view – tap on the Format line to choose which one you prefer, then enter the lat/lon below.
Many newer portable GPSs allow you to choose which format is used, so if you fly with a Garmin 760 and an iPad, for example, you could use degree decimal for both. Just use the Tools menu from the main menu on the Garmin to adjust the settings.
So latitude and longitude coordinates are both simple and confusing. Take some time to understand what format your main map sources use. Once you know that, entering user waypoints or flying direct to a lat/lon coordinate is really pretty simple.
There are also a number of free websites that help you convert from one format to another. This one is our favorite.