Reading a Sectional Chart

A sectional aeronautical chart is the standard reference document for visualizing airspace, obstacles and airport information across a region. Airspace apps used for LAANC and general flight planning are built on top of this same underlying data, presented more simply. Learning to read a sectional directly is not required for recreational flying, but it is directly tested on the Part 107 exam, and it builds an intuition for airspace that makes every app you use afterward make more sense.

The first concept: MSL vs AGL

Almost every altitude printed on a sectional chart is expressed in MSL, mean sea level, a fixed reference that does not change with terrain. Drone altitude limits, by contrast, are almost always expressed in AGL, above ground level, meaning height above the terrain directly beneath the aircraft at that moment. In flat terrain near sea level the two numbers track closely, but in hilly or mountainous terrain they diverge significantly. A Class E floor printed as 3,500 feet MSL over terrain sitting at 2,800 feet elevation only leaves 700 feet of AGL clearance before entering controlled airspace, a fact that is invisible if you only look at the MSL number without checking the ground elevation underneath it.

Airspace class colors and line styles

Each controlled airspace class uses a consistent color and line style on every sectional chart, which is the fastest way to identify what kind of airspace you are looking at without reading every label.

Sectional chart airspace symbology

Airspace class	Chart symbol	Typical use
Class B	Solid blue rings	Major international airports
Class C	Solid magenta rings	Mid-size airports with a control tower
Class D	Dashed blue circle	Smaller towered airports
Surface Class E	Dashed magenta circle	Non-towered airport with instrument approaches
Class E starting below 1,200 ft AGL	Shaded magenta area, no circle	Extended approach corridor, easy to miss
Class G	No shading, uncontrolled by default	Everywhere not otherwise marked

Class B and C: the rings that step down

Class B airspace around the busiest airports is typically drawn as a series of concentric rings, often described informally as an upside-down wedding cake, where the floor altitude of the controlled airspace rises with distance from the airport center. Class C follows a similar but smaller stepped pattern. What matters practically for a drone pilot is that being outside the outermost ring does not guarantee you are clear of controlled airspace if you are flying at altitude, since the boundary steps outward and upward simultaneously. This is exactly the kind of detail an airspace app resolves automatically for your specific coordinates, but understanding the shape helps you sanity-check what the app shows you.

Class D and the transition into Class E

Class D airspace, drawn as a dashed blue line, surrounds smaller towered airports and typically extends from the surface up to a published ceiling, often around 2,500 feet AGL. Just outside a Class D boundary, airspace often transitions into surface Class E to support instrument approaches, shown with a dashed magenta line. The easy mistake is assuming that stepping outside the dashed blue Class D circle means you are in uncontrolled airspace; frequently you have simply stepped into a different controlled class rather than out of controlled airspace entirely.

Why this matters even with an app doing the work

An airspace authorization app will tell you directly whether a specific location and altitude needs LAANC or is clear to fly, and for a single flight that is the tool to trust over manual chart reading. But understanding the underlying chart symbology helps in a few concrete ways: it lets you sanity-check an app result that looks surprising, it helps you understand why a location a few hundred feet away carries a different rule, and for Part 107 candidates, it is directly examinable material covered further in how to study for Part 107.

Obstacle and terrain symbols worth recognizing

Beyond airspace classes, sectionals mark obstacles that matter directly to low-altitude drone flight even though they are drawn primarily for manned aviation. Towers, including communication and radio towers, appear as small tower icons with their height printed alongside, often both in MSL and in AGL, and are worth cross-referencing directly against your planned flight altitude, since some towers extend well above the general 400 foot drone altitude limit. Terrain elevation is shown through contour lines and shaded relief in mountainous areas, along with maximum elevation figures printed in a grid across the chart, which is the fastest way to sanity-check how much AGL clearance a given MSL altitude actually provides in hilly terrain, tying directly back to the MSL-versus-AGL distinction covered above.

How chart data flows into the apps most pilots actually use

Nearly every airspace and LAANC app used for drone flight planning is built on the same underlying aeronautical data that produces the printed sectional, refreshed on a regular publication cycle and supplemented with real-time layers like TFRs and NOTAMs that a static chart cannot show. This is worth understanding because it explains a common point of confusion: two different apps occasionally show slightly different visual styling for the same airspace, since each developer makes their own presentation choices, but the underlying boundaries and altitudes should trace back to the same authoritative source data. If two apps ever meaningfully disagree about whether a location requires authorization, that is worth investigating directly rather than picking whichever answer is more convenient, since one of the two is working from stale or misconfigured data.

Understanding the base chart also helps when an app's simplified visual summary leaves out a detail that matters for a specific flight, such as a nearby glider operations area or a parachute jump zone, both of which appear on a full sectional but are sometimes abbreviated or omitted in a simplified drone-specific app view. For any flight near an airport with unusual local activity, cross-referencing the full sectional or a detailed briefing source alongside your primary drone app is a reasonable extra step rather than relying on a single simplified summary.

Special use airspace: a different category entirely

Sectionals also mark special use airspace, including restricted areas, military operations areas, and warning areas, typically shown with a distinct hatched or outlined boundary and a identifying label. These are not part of the standard Class B through G system and carry their own access rules, often involving military or government activity that makes the airspace unpredictable or entirely off-limits during active use. A drone flight near this kind of boundary needs the same live-data verification through a current airspace app that any controlled airspace flight needs, since a chart alone cannot tell you whether a specific restricted area is active on the day and time you plan to fly.

Putting it together with the rest of the airspace picture

Sectional charts are one piece of a larger airspace picture that also includes TFRs, which are not permanent features of the chart and only appear through a live briefing or app, and the UAS Facility Map grid ceilings that govern LAANC approval, which are a separate data layer overlaid on top of the base airspace classes. See the airspace classes reference for a compact summary of every class side by side, and revisit the preflight checklist for where an airspace check fits into your routine before every flight.