2.8 Latitude, Longitude, and Navigation

Latitude, Longitude, and Navigation

Reading coordinates lets you pinpoint a site on a sectional, interpret the center point of a TFR NOTAM, and answer the test's location questions. Drone pilots do not navigate cross-country, but the exam still expects fluency with the coordinate grid and altitude references.

Latitude

Latitude measures angular distance north or south of the equator:

• Range 0 degrees (equator) to 90 degrees N/S (poles).
• Lines of latitude run east-west and are called parallels.
• On a sectional, latitude increases northward (toward the top).
• The contiguous U.S. spans roughly 24 N to 49 N.

Longitude

Longitude measures angular distance east or west of the Prime Meridian at Greenwich, England:

• Range 0 degrees to 180 degrees E/W.
• Lines of longitude run north-south, converge at the poles, and are called meridians.
• On a U.S. sectional, longitude increases westward (toward the left).
• The contiguous U.S. spans roughly 67 W to 125 W.

Coordinate Formats

Sectionals are tick-marked in minutes (60 minutes per degree), so the degrees-minutes format is most common when you read a position on the chart.

Reading Coordinates Step by Step

1. Locate the latitude lines (horizontal) and their degree labels on the sides.
2. Locate the longitude lines (vertical) and their labels on the top and bottom.
3. Count tick marks between labeled lines; each tick equals 1 minute.
4. Read latitude first (N or S of the nearest parallel), then longitude (E or W of the nearest meridian).

Memory aids: "Latitude is a Ladder" — the rungs lie flat, east-west, like parallels. Longitude lines are the long lines running pole to pole.

Magnetic Variation (Declination)

Sectionals show the angle between true north and magnetic north with dashed isogonic lines labeled, for example, "10 degrees E" or "15 degrees W." The agonic line is where variation is zero.

• East variation: magnetic north lies east of true north, so the magnetic heading is less than the true heading.
• West variation: magnetic north lies west of true north, so the magnetic heading is more than the true heading.

Rule: "East is Least, West is Best" — subtract east variation from a true heading, add west variation.

Worked example: to fly a true course of 090 degrees where the chart shows 10 degrees east variation, subtract: 090 minus 10 equals a 080-degree magnetic heading. With 10 degrees west variation you would add to get 100 degrees.

Altitude References

The Part 107 400-foot ceiling is measured in AGL. Standing on a hill at 2,000 ft MSL and flying 400 ft above it puts the drone at 2,400 ft MSL but only 400 ft AGL — which is legal. An exception allows flight higher than 400 ft AGL when within 400 feet of a structure (and no more than 400 ft above the structure's immediate uppermost limit), useful for tower inspections.

Common Traps

• Swapping latitude and longitude — read latitude (N/S) first.
• Reversing the variation rule; "East is Least" means subtract.
• Treating the 400 ft ceiling as MSL; it is always AGL relative to the ground below the drone.

Why MSL vs AGL Trips Up Drone Pilots

The single most consequential altitude concept on the exam is the difference between MSL and AGL, because the two references serve different masters. Charts, airspace floors and ceilings, and your aircraft's altimeter all speak in MSL so that every aircraft shares a common datum regardless of the terrain below. The Part 107 ceiling, by contrast, is fixed in AGL because the rule's purpose is to keep drones below the airspace where manned aircraft operate, and that buffer must hold whether you launch from a beach or a mountain ridge.

A pilot who confuses the two might think flying from a 3,000 ft MSL plateau means a 400 ft MSL ceiling, which would be nonsensical; the correct reading is 400 ft above the ground beneath the drone, or about 3,400 ft MSL.

The Structure Exception in Practice

The regulation includes a practical relief valve: a drone may fly higher than 400 ft AGL when operating within 400 feet of a structure, provided it stays no more than 400 ft above the structure's immediate uppermost limit. This is what makes tower, antenna, and tall-building inspections legal — a 1,000 ft broadcast tower can be inspected from top to bottom by hugging within 400 ft of it. The exam may test whether you understand that this exception is tied to proximity to the structure, not a blanket permission to climb. Drift away from the structure and the standard 400 ft AGL ceiling snaps back into force.

Worked Scenario

You stand on a hill at 1,800 ft MSL and need to confirm your maximum legal altitude. Without a structure nearby, the ceiling is 400 ft AGL, putting your drone at about 2,200 ft MSL at the top of its envelope. Now add a 250 ft cell tower at your location: while inspecting it within 400 ft of the structure, you may climb to 400 ft above its 250 ft tip — roughly 2,450 ft MSL — but only while staying close to the tower. Step the drone laterally away from the tower and you must descend back to 400 ft AGL. Converting between MSL and AGL fluently, and knowing when the structure exception applies, is exactly what these navigation questions probe.