Every sectional aeronautical chart is far more than a road map with airports drawn on it. It is a sophisticated topographic document that communicates the shape and elevation of the terrain beneath the airspace. For a Remote Pilot Certificate applicant — and for any certificated remote pilot conducting real-world drone operations under 14 CFR Part 107 — being able to read that terrain information quickly and accurately is a genuine safety skill. A small unmanned aircraft system (sUAS) operating at 400 feet above ground level (AGL) can be much closer to a ridge or antenna than the pilot realizes if the underlying terrain is not understood. This article explains every major method sectional charts use to depict topography, the numbers you need to know for the FAA Knowledge Test, and the practical habits that keep flights safe.
Sectional charts are published at a scale of 1:500,000 (one inch equals approximately 6.86 statute miles (approximately 5.97 nautical miles)) and are updated every 56 days. They are produced under the authority of the FAA and the National Geospatial-Intelligence Agency (NGA), and their content conventions are standardized so that any pilot in the United States reads them the same way. The aeronautical portion of the chart — airways, airspace boundaries, frequencies — gets most of the attention in ground school, but the topographic layer underneath it is equally important, especially at low altitudes where terrain and obstacles pose the greatest collision risk.
How Topographic Shading Works
The most immediately noticeable terrain feature on a sectional chart is the elevation color tinting, sometimes called hypsometric tinting or terrain shading. The chart uses a graduated color palette that runs from green at low elevations through increasingly warm tones — tan, light brown, darker brown — as elevation rises, culminating in reddish-brown or gray for the highest terrain. The specific color bands correspond to elevation ranges printed in the chart legend, and those ranges are expressed in feet above mean sea level (MSL). Green does not simply mean flat; it means the terrain falls within a relatively low elevation band (often 0–1,000 feet MSL on most sectionals, though this varies by chart). Conversely, a patch of dark brown terrain tells you at a glance that the ground is significantly elevated, even before you read a single number.
This color gradient is a rapid situational awareness tool. When you are planning a drone flight and you look at the sectional, a quick scan of color tells you whether your operational area is in a valley (light green), on a plateau (tan or brown), or near high terrain that might require you to reconsider your planned altitude or route. Remember: Part 107 limits sUAS operations to a maximum of 400 feet AGL, or up to 400 feet above a structure if within 400 feet of that structure. If the terrain itself rises 800 feet MSL over a short distance, your 400-foot AGL ceiling means you could be operating at 1,200 feet MSL on one side of a ridge and only 800 feet MSL on the other — without changing your indicated altitude at all.
Contour Lines: Reading the Shape of the Land
Overlaid on the color tinting are contour lines — brown lines that connect all points of equal elevation. Every point on a given contour line is at exactly the same height above mean sea level. The contour interval — the difference in elevation between adjacent contour lines — is printed in the chart legend and is typically 500 feet on standard sectional charts, though some charts use a different interval where terrain is relatively flat or extremely rugged. Every fifth contour line is printed as a heavier line called an index contour, and these are usually labeled with their elevation in feet MSL to anchor your interpretation.
The spacing between contour lines tells you the steepness of terrain. When contour lines are packed tightly together, the terrain rises sharply — you are looking at a steep slope or cliff. When contour lines are spread far apart, the terrain changes elevation gradually over a long distance — a gentle slope or plain. A hill appears as a series of roughly concentric closed contour lines, each inner ring at a higher elevation than the one surrounding it. A valley or canyon appears as contour lines that form a V or U shape pointing toward higher ground.
For a remote pilot, steep terrain — indicated by closely-spaced contours — should trigger concern about terrain-induced turbulence, unpredictable wind shear, and reduced GPS signal quality (due to satellite geometry blocked by high terrain on one side). Flat terrain with widely-spaced contours is more forgiving of altitude management errors but may still contain man-made obstacles that contour lines do not show.
Maximum Elevation Figures
Within each quadrant of latitude and longitude on a sectional chart — each one-degree-by-one-degree square of airspace — you will find a bold blue number called the Maximum Elevation Figure (MEF). The MEF represents the highest terrain or obstacle in that quadrant, determined by adding a 200-foot buffer for obstacles (or 100 feet if the obstacle's true elevation is well known) to the highest known terrain/obstacle elevation, then rounding up to the next 100-foot increment. The MEF is expressed in thousands and hundreds of feet MSL: a large digit followed by a smaller digit. For example, an MEF printed as "4 2" means 4,200 feet MSL is the highest feature in that quadrant after the safety buffer is applied.
The MEF is the single most important terrain-related number on the sectional chart for flight planning. A drone remote pilot can use the MEF to quickly determine the minimum MSL altitude needed to clear all terrain and obstacles in a given area. Equally important: if the local ground elevation is known, subtracting that from the MEF gives a rough sense of how much vertical clearance exists and whether a 400-foot AGL flight will remain below the MEF with comfortable margin.
Spot Elevations and Benchmark Symbols
At prominent high points — mountain peaks, hilltops, and notable ridges — sectional charts mark the precise elevation of that specific point. A spot elevation appears as a small black dot (or an X) accompanied by a number in feet MSL, printed in black. The highest spot elevation in each latitude/longitude quadrant is printed in a bold, enlarged font to make it stand out from surrounding spot elevations. Survey benchmarks — permanent markers established by the U.S. Geological Survey or other agencies — appear as small triangles with an elevation figure and the letters "BM" or similar notation.
Spot elevations are especially useful when working near mountainous terrain where the highest obstacle might be a rocky summit rather than a tower. They complement the MEF by giving precise elevation data at specific geographic points.
Obstruction Symbols
Man-made vertical obstacles — towers, antennas, wind turbines, buildings — are depicted by specific symbols on sectional charts. A single obstacle is shown with a small symbol (the exact shape varies by obstacle type) accompanied by two numbers stacked vertically: the top number is MSL elevation of the obstacle's highest point, and the bottom number in parentheses is the AGL height of the obstacle above the terrain immediately beneath it. Obstruction symbols vary in shape to distinguish types of obstacles (including group obstructions), and lighting requirements are governed separately by FAA obstruction marking and lighting standards (AC 70/7460-1) rather than by a fixed 1,000-foot AGL open/filled symbol threshold. Groups of closely-spaced obstacles are depicted with a group obstruction symbol.
For Part 107 operations, obstruction symbols deserve extra attention because your 400-foot AGL ceiling is measured from the ground directly beneath your aircraft, not from sea level. An antenna shown as 350 feet AGL is below your ceiling — but only if the terrain around it is flat. If that antenna sits on a hillside, the effective clearance changes as you approach from different directions.
Why Terrain Awareness Matters for Part 107
Unlike manned aircraft, a drone does not have a barometric altimeter that the pilot reads in real time from a cockpit. Most consumer and commercial sUAS use GPS-based altitude, which is referenced to the WGS-84 ellipsoid and may differ from MSL elevation by a significant amount depending on location. Some systems provide AGL altitude by subtracting a stored terrain database value — but that database may be coarse or outdated. The practical result is that a remote pilot must cross-reference the chart, understand the terrain, and apply conservative operating practices. Misreading a terrain color band or ignoring a spot elevation can mean the aircraft collides with a ridge or antenna that appeared safely below the operational ceiling on paper.
Key Numbers and Rules
- Sectional chart scale: 1:500,000 (approximately 6.86 statute miles per inch)
- Update cycle: Every 56 days
- Standard contour interval: 500 feet MSL (verify in chart legend)
- MEF buffer: 200-foot buffer added for obstacles (100 feet if elevation is well known), then rounded up to next 100 feet
- MEF format: Large digit = thousands of feet MSL; small digit = hundreds of feet MSL
- Obstacle symbols: Shape varies by obstacle type and includes group obstruction symbols; lighting requirements are set by AC 70/7460-1, not chart symbol fill
- Part 107 altitude limit: 400 feet AGL (or 400 feet above a structure if within 400 feet of it)
- Hypsometric tinting: Green = low elevation; progressively warmer colors = higher elevation; ranges printed in chart legend
Memory Aid
Use the phrase "Colors, Contours, Crests, and Clearances" as a pre-flight chart-reading checklist for terrain:
- Colors — Scan the hypsometric tint in your operational area. Is the terrain low and green or high and brown?
- Contours — Look at contour line spacing. Are they tight (steep slopes, turbulence risk) or spread out (gentle terrain)?
- Crests — Find the bold spot elevation and the MEF for your quadrant. Know the highest point.
- Clearances — Confirm your planned operating altitude keeps you above all depicted obstacles and terrain with margin to spare.
Common Test Traps
- Confusing MSL and AGL: The MEF, spot elevations, and the top obstruction number are all MSL. The parenthetical obstruction number is AGL. Mixing these up is the single most common topography error on FAA Knowledge Tests.
- Assuming green means flat: Green tinting means low elevation relative to the chart's color scale — it does not mean the terrain is featureless. A 600-foot hill in an otherwise low region may still appear green but still represents a real obstacle to a 400-foot AGL drone.
- Ignoring the chart legend: The contour interval and elevation color ranges are printed in the legend and vary between chart editions and geographic areas. Never assume the standard 500-foot interval without checking.
- Treating the MEF as a clearance guarantee: The MEF includes buffer, but it does not account for obstacles added or modified after the chart's 56-day publication cycle. Always cross-reference with current NOTAMs and the FAA's UAS Data Delivery System (LAANC/DroneZone).
- Missing the dual-number obstruction format: On the Knowledge Test, questions often show an obstruction with two numbers and ask which is MSL and which is AGL. Remember: top number = MSL, bottom number in parentheses = AGL — every time.