2.8 Latitude, Longitude, and Navigation
Key Takeaways
- Latitude runs east-west (parallels), longitude runs north-south (meridians) — remember "Latitude = Ladder."
- In the US, latitude increases going north and longitude increases going west on charts.
- The Part 107 400-foot altitude limit is measured AGL (Above Ground Level), not MSL.
- Magnetic variation: "East is Least" (subtract from true heading), "West is Best" (add to true heading).
- MSL is used on altimeters and charts; AGL is used for Part 107 limits and obstruction heights.
2.8 Latitude, Longitude, and Navigation
Understanding geographic coordinates is essential for reading sectional charts, interpreting NOTAMs, and communicating locations on the exam. Several test questions require you to identify locations using latitude and longitude.
Latitude
Latitude measures the angular distance north or south of the equator:
- Range: 0° (equator) to 90° N/S (poles)
- Lines of latitude run east-west (parallel to the equator)
- Also called parallels
- On sectional charts, latitude increases as you move north (up)
- The contiguous US spans approximately 24°N to 49°N
Longitude
Longitude measures the angular distance east or west of the Prime Meridian (Greenwich, England):
- Range: 0° (Prime Meridian) to 180° E/W
- Lines of longitude run north-south (converging at the poles)
- Also called meridians
- On sectional charts covering the US, longitude increases as you move west (left)
- The contiguous US spans approximately 67°W to 125°W
Coordinate Format
Coordinates can be expressed in several formats:
| Format | Example | Precision |
|---|---|---|
| Degrees (D) | N33° W118° | ~69 miles |
| Degrees-Minutes (DM) | N33°45' W118°20' | ~1.15 miles |
| Degrees-Minutes-Seconds (DMS) | N33°45'30" W118°20'15" | ~100 feet |
On sectional charts, the DM (degrees-minutes) format is most commonly used.
Reading Coordinates on Sectional Charts
Step-by-step process:
- Identify the latitude lines — horizontal lines with degree numbers on the sides
- Identify the longitude lines — vertical lines with degree numbers on top/bottom
- Find your position — count the tick marks between degree lines (each tick = 1 minute)
- Read latitude first — N/S of the nearest labeled parallel
- Read longitude second — E/W of the nearest labeled meridian
Memory Aid: Latitude = "Ladder" (the rungs go side to side, like latitude lines). Longitude = "Long" (the lines are long, running from pole to pole).
Magnetic Variation (Declination)
Sectional charts show the difference between true north and magnetic north using isogonic lines:
- Isogonic lines — dashed lines labeled with the magnetic variation (e.g., "10°E" or "15°W")
- Agonic line — the line where variation is 0° (magnetic and true north are the same)
- East variation: Magnetic north is east of true north — magnetic heading is LESS than true heading
- West variation: Magnetic north is west of true north — magnetic heading is MORE than true heading
Memory Aid: "East is Least, West is Best"
- East variation: magnetic heading is LEAST (subtract from true heading)
- West variation: magnetic heading is BEST (add to true heading)
Altitude References
Understanding altitude terminology is critical:
| Term | Definition | Usage |
|---|---|---|
| MSL (Mean Sea Level) | Height above average sea level | Used on altimeters, charts, airspace boundaries |
| AGL (Above Ground Level) | Height above the terrain directly below | Used for Part 107 altitude limits, obstruction heights |
| Indicated Altitude | What the altimeter reads | Set to local altimeter setting |
| Pressure Altitude | Height above the standard pressure datum (29.92" Hg) | Used for density altitude calculations |
| Density Altitude | Pressure altitude corrected for non-standard temperature | Affects aircraft performance |
The Part 107 400-foot limit is measured in AGL — not MSL. If you are on a hilltop at 2,000 ft MSL and fly 400 ft above it, you are at 2,400 ft MSL but 400 ft AGL — which is legal.
Practical Navigation for Drone Pilots
While drone pilots do not navigate long distances, understanding navigation helps with:
- Identifying your location on a sectional chart for airspace determination
- Reading coordinates in NOTAMs and TFRs
- Understanding altimeter settings for altitude reporting
- Communicating with ATC (if needed for authorization) using proper terminology
Lines of latitude run in which direction?
The Part 107 altitude limit of 400 feet is measured in:
With an east magnetic variation of 10°, to fly a true course of 090°, your magnetic heading would be: