How to read FAA sectional charts
Decode airspace lines, shelf altitudes and MSL versus AGL on FAA sectional charts, then check your interpretation in 3D.
Read a sectional as several layers of information
A sectional combines terrain, obstacles, airports, navigation information and airspace. For an airspace question, first locate the aircraft horizontally, then read the boundary style, then find the floor and ceiling for that specific sector. Only after that should you decide which operating rule applies. The reference for the symbols below is the FAA Aeronautical Chart Users’ Guide, VFR terms and symbols.
| Marking | Meaning | Read next |
|---|---|---|
| Solid blue | Class B boundary | The sector’s ceiling and floor in hundreds of feet MSL |
| Solid magenta | Class C boundary; a labeled equipment veil is a different use of a magenta line | Sector limits and nearby annotations, not color alone |
| Dashed blue | Class D boundary | Boxed MSL ceiling, minus sign if present, and effective-time notes |
| Dashed magenta | Class E surface boundary | Surface-area or extension context and applicable notes |
| Faded magenta band | Class E floor of 700 feet AGL on the shaded side | Other overlapping airspace and the floor on the other side |
| Faded blue band | Class E floor of 1,200 feet AGL on the shaded side | Adjacent airspace and any higher-floor labels |
Do not confuse a faded band with a dashed surface boundary. They describe different floors. Likewise, the magenta Mode C/ADS-B equipment veil does not turn everything inside it into Class C. Read the label attached to a line before interpreting it.
Convert the number, then keep its reference
A hypothetical stacked 80/25 shelf label gives an 8,000-foot MSL ceiling and a 2,500-foot MSL floor. SFC means surface. Class D uses a boxed ceiling rather than the same stacked shelf notation; a minus sign excludes the stated ceiling altitude. For a Class C ceiling marked T, the top is up to, but not including, the floor of the overlying Class B.
Charted obstacle elevations use MSL, with AGL heights in parentheses when provided. AGL and MSL are not interchangeable: terrain elevation changes across a route, so a constant MSL altitude does not give a constant height above the ground. Keep the unit and reference beside every number in your notes.
Worked example: compare an airplane to a shelf
Suppose a blue sector is labeled 80/25. The airplane is at 2,000 feet MSL and the terrain beneath it is 600 feet MSL. Its approximate height above that terrain is 1,400 feet, but that subtraction is unnecessary for the shelf comparison: 2,000 MSL is below the 2,500 MSL floor. At 3,000 MSL, the same horizontal position is within the shelf’s vertical limits.
Does “below the shelf” identify the airspace underneath?
No. Look for any underlying Class C, D or E designation and its limits; do not automatically label the airspace Class G. The shelf label answers where that shelf begins, not every question about what lies below it.
Use 3D to check your interpretation
- Open the sectional and airspace probe. Choose one location and write down the boundary style, floor, ceiling and altitude reference before reading the result.
- Rotate the 3D view and compare the volume with your written prediction. If they disagree, return to the chart’s legend and sector labels.
- Try 3D spot questions to practice reading limits at another location.
AirspaceLab’s map is an educational visualization. This lesson does not establish the effective date of its chart tiles. For real flight preparation, verify the chart edition and consult current NOTAMs and the Chart Supplement; a displayed image cannot confirm that every restriction or facility status is current.
FAA references
- FAA AIM, Chapter 3, Section 2: controlled airspace - operational explanations for Classes B, C and D.
- FAA Aeronautical Chart Users’ Guide - July 9, 2026 edition, VFR terms and symbols. Use the FAA index for later editions.