Latitude/Longitude on Charts: Decimal Degree Conversion Trick
Degrees-minutes-seconds vs decimal degrees confuses everyone. Here's how to convert between them and why it matters for drone pilots.
When studying for your Part 107 test, you’ve probably stared at a sectional chart and felt overwhelmed. Along the edges of the map are numbers that pinpoint exactly where you are. The tricky part? Sectional charts speak one language, but your drone apps speak another.
Latitude: The Rungs of the Ladder
Latitude lines run horizontally across your sectional chart — these are called parallels. They measure distance north or south of the equator. The equator is zero degrees. As you move toward the North Pole, numbers increase to 90 degrees.
An easy way to remember: think of a ladder. The rungs go across, just like latitude lines.
Longitude: The Vertical Lines
Longitude lines run vertically from top to bottom — these are meridians. They measure distance east or west of the Prime Meridian in Greenwich, England (zero degrees). Moving west across the US, numbers increase. The West Coast sits around 120 degrees West.
The Two Formats That Confuse Everyone
Sectional charts use degrees-minutes-seconds (DMS). Think of it like telling time: 60 minutes in a degree, 60 seconds in a minute. A coordinate might read: 38 degrees 45’ 30” N (38 degrees, 45 minutes, 30 seconds North).
But drone apps — LAANC grids, DJI Fly, Google Maps — use decimal degrees (DD). That same location becomes 38.758333.
Why This Matters
Mix up formats and you could put yourself in the wrong airspace. NOTAMs and TFRs publish coordinates in DMS. If you type those directly into your drone app, it drops a pin in the wrong location — or rejects the input entirely.
The Conversion Trick
Remember two division facts: divide minutes by 60, divide seconds by 3600.
Example: A TFR boundary is listed as 34 degrees 12’ 18” N.
- Degrees: 34
- Minutes: 12 / 60 = 0.20
- Seconds: 18 / 3600 = 0.005
- Decimal degrees: 34 + 0.20 + 0.005 = 34.205
That’s it. Type 34.205 into your app and you have the exact right spot.
Going the other direction? Take the decimal part, multiply by 60 for minutes, then multiply the remaining decimal by 60 for seconds. But as a drone pilot, you’ll almost always go from chart format to app format — so just remember divide by 60 and divide by 3600.
How Much Ground Does One Degree Cover?
Latitude: One degree always equals about 69 miles, whether you’re in Florida or Alaska.
Longitude: This varies because meridians squeeze together at the poles. At the equator, one degree of longitude is also about 69 miles. In Seattle (~47 degrees north), it’s only about 47 miles. This is why grid squares on sectional charts look stretched and tall the further north you go.
Knowing how to read coordinates on a chart and convert them to the decimal degrees your tablet expects keeps you out of restricted airspace, ensures LAANC authorizations match your actual flight area, and makes pre-flight planning way less stressful.
Our free Part 107 Course covers sectional charts, coordinates, and every other chart topic on the exam.
