15.1 Sectional Chart Symbology and Airspace Depiction

ACS PA.I.D and PA.VI.A assume you can extract a route from a current VFR Navigation Chart, not just name the colors. The official decoder is the FAA Aeronautical Chart User’s Guide. PHAK Chapter 16 and the AIM tell you how to use what you decoded. This section is depiction. Legal entry, weather, and transponder rules live in Chapter 5; do not invent a new Class B clearance rule from a blue line.

Scale, latitude/longitude, and tick marks

A Sectional Aeronautical Chart is 1:500,000. One inch on the paper is 500,000 inches on the Earth, about 6.86 nautical miles (instructors round that to 7 NM per inch). A VFR Terminal Area Chart (TAC) over a busy Class B complex is 1:250,000, about 3.43 NM per inch. Use the TAC when the wedding-cake shelves, VFR flyways, and airport names are stacked too tightly on the sectional. World Aeronautical Charts at 1:1,000,000 are discontinued; do not plan a PAR answer around a WAC.

Charts are oriented to true north. Parallels of latitude run east–west; meridians of longitude run true north–south. Tick marks on the neatline and on the 30-minute grid let you plot a latitude/longitude to the nearest minute. One minute of latitude is one nautical mile, so the latitude scale on the side of the chart is the honest distance scale. Measuring a long east–west leg with a cheap plotter on the longitude scale is how students invent a 12-percent error.

Isogonic lines

Dashed magenta isogonic lines connect points of equal magnetic variation. Each line is labeled (for example 4°W or 12°E). The agonic line is the 0° line. Variation changes slowly as the magnetic pole moves; the number printed on the current chart cycle is the number you apply. You do not “update” a 2018 memory of local variation onto a 2026 chart. Section 15.3 turns that printed number into a magnetic heading.

Maximum Elevation Figure — how the FAA computes it

The Maximum Elevation Figure (MEF) is the large blue two-digit number (thousands and hundreds of feet MSL; the last two zeros are omitted) in each quadrangle bounded by the ticked 30-minute latitude and 30-minute longitude lines. A printed 38 means 3,800 feet MSL. The MEF is the highest of terrain and vertical obstacles in that box after the Chart User’s Guide procedure. It is a worst-case elevation figure, not a recommended cruise altitude and not a 91.119 clearance guarantee.

Aeronautical Information Specialists use two procedures. When a man-made obstacle is more than 200 feet above the highest terrain in the quadrant:

1. Take the top of the obstacle in feet MSL.
2. Add the possible vertical error of the source — normally 100 feet (or one-half the source contour interval when that interval exceeds 200 feet).
3. Raise the result to the next higher 100-foot level.

Official Chart User’s Guide example: obstacle top 2,424 + 100 = 2,524 → raise to 2,600. The MEF prints as 26.

When a natural terrain feature or natural vertical obstacle (a tree, a ridge) is the highest feature:

1. Take the elevation of the feature.
2. Add the same 100-foot (or half-contour) source-error value.
3. Add a 200-foot allowance for uncharted or man-made obstacles that chart specifications do not require to be portrayed.
4. Raise to the next higher 100-foot level.

Official example: terrain 3,448 + 100 = 3,548 + 200 = 3,748 → raise to 3,800. The MEF prints as 38.

The street mnemonic “highest thing + 100 or + 200, then round up 100 feet” is that pair of procedures, not a third formula. Do not add 200 feet to a tower that is already the controlling man-made obstacle. Do not treat the MEF as the elevation of the single peak you can see — the peak plus trees plus source error plus rounding is why 3,448 of dirt becomes 38 on the chart.

Airport symbology — color, surface, lighting, CT and frequency

Airports with control towers, and their data, are blue. All others, and their data, are magenta. Color is tower versus no tower, not hard versus soft and not civil versus military. Military fields use the same color rule plus distinctive runway or airfield symbols.

Public-use airport symbols (Chart User’s Guide):

• Hard-surfaced runway 1,500 to 8,069 feet: filled circle with the runway pattern inside.
• Hard-surfaced runway longer than 8,069 feet, or some multiple hard runways shorter than 8,069 feet: the runway outline itself, without the simple filled circle.
• Other than hard-surfaced: open circle, no runway drawing.
• Seaplane bases, heliports, ultralight fields, and private airports have their own ticks and labels.

The data block next to the symbol is compressed on purpose. A typical towered block reads like CT − 118.3 ATIS 124.6 on one line and 472 L 70 122.95 on the next: field elevation 472 feet MSL, lighting information, longest runway 7,000 feet (the chart prints length in hundreds of feet), and the UNICOM or CTAF. CT is the control-tower frequency. A star after the CT frequency means the tower is part-time — when it is closed, the Chart Supplement “Airspace” line tells you whether the dashed-blue surface area reverts to Class E or Class G, and the CTAF becomes the frequency you actually use. L or a lighting tick means lights exist; an asterisk (*) means lighting limitations — hours, pilot-controlled lighting, or intensity — and you must open the Chart Supplement. A star at the airport symbol is a rotating beacon in sunset-to-sunrise operation.

You cannot read runway width, displaced thresholds, fuel grade, attendance, or the full lighting story from the sectional block. That is why ACS PA.I.D.S2 pairs the chart with the Chart Supplement.

Airspace line styles, obstacles, terrain, SUA, and MTRs

Terrain uses contour lines, hypsometric tint, and spot elevations. Obstacles are towers or groups: unlighted versus lighted (lightning-bolt or star), group obstacles, highest-in-group, and UC for under construction. Elevations are MSL with AGL in parentheses. A 1,200-foot tower next to a 1,500-foot MEF is not a contradiction — the MEF already includes the rounding and error stack.

Restricted and prohibited areas are blue-hatched. MOAs and alert areas are magenta-hatched. Times, altitudes, and the controlling agency sit in the chart margin; temporary MOAs and temporary restricted areas are not on the sectional. Military training routes are the thin gray IR (IFR) and VR (VFR) lines. AIM 3-5-2: a route with no segment above 1,500 feet AGL uses four digits (VR1207) — the whole route is at or below 1,500 AGL. A route with one or more segments above 1,500 feet AGL uses three digits (VR207). Four digits means low and close. You may cross an MTR; treat the line as a corridor that can be miles wide and ask Flight Service for times.

Chart Supplement as companion

The Chart Supplement (the old Airport/Facility Directory) is not optional decoration. It carries airport sketches, runway length and width, lighting and PCL codes, TPA, fuel, oxygen, attendance, FSS, ASOS/AWOS phone and frequency, remarks, and the SUA times the sectional margin only sketches. PAR items that ask “how long is the lighted portion” or “is 100LL available after 1800” are Chart Supplement items. Fly the current chart cycle; a faded 2023 sectional in the seat-back pocket is how you miss a new tower and a new dashed-blue ring.

PAR scenario: the quadrangle west of your destination prints MEF 26. The highest charted tower in that box is 2,424 MSL. That is the official man-made example: 2,424 + 100 = 2,524, raised to 2,600. Cruising at 2,500 MSL because “the tower is only 2,424” is below the MEF and is not a plan. Pick a 91.159 altitude that also sits comfortably above the MEF, then confirm the destination’s CT frequency, lighting asterisk, and fuel in the Chart Supplement — not from the three-digit runway number alone.