Maximum Elevation Figure (MEF) (the official calculation)
John J. Miller
John J. Miller
jo...@mcdata.com
"Maximum Elevation Figure (MEF)
Recently, several pilots have asked the Office of Aeronautical Charting &
Cartography (AC&C) how the Maximum Elevation Figure (MEF) is calculated.
The MEF represents the highest elevation, including terrain and other vertical
obstacles (towers, trees) within the 'boxes' defined by ticked lines of
latitude and longitude. On the Sectional chart, these 'boxes' are 30 minutes
by 30 minutes. The MEF is depicted to a 100 foot value (the last two digits
of the number are not shown). Calculation of the MEF differs between man-made
obstacles and natural terrain/vertical obstacles.
When a man-made obstacle is more that 200 feet above the highest terrain
within the 'box', the cartographer takes the following steps:
1. Determine the elevation of the top of the obstacle above mean sea level.
2. Add the possible vertical error of the source material to the above figure
(100 feet or ½ the contour interval when interval on source exceeds 200 feet.
U.S. Geological Survey Quadrangle Maps with contour intervals as small as 10
feet are normally used).
3. Round the resultant figure up to the next higher hundred foot level.
When a natural terrain feature or natural vertical obstacle (e.g. a tree) is
the highest feature within the 'box', the cartographer takes the following
steps:
1. Determine the elevation of the base of the feature above mean sea level.
2. Add the possible vertical error of the source material to the above figure
(100 feet or ½ the contour interval when interval on source exceeds 200 feet).
3. Add a 200 foot allowance for natural or man-made obstacles which are not
portrayed because they are below the minimum height at which the chart
specifications require their portrayal (on Sectionals, obstacles 200 feet and
less are not required to be portrayed).
4. Round the resultant figure up to the next higher hundred foot level.
MEF data is based on the best information available to the cartographer. The
most current MEF data is contained in the appropriate Airport/Facility
Directory Aeronautical Chart Bulletin Section.
The above information is also contained in AC&C's Aeronautical Chart User's
Guide, 4th Edition. The User's Guide explains all the symbols used on VFR and
IFR charts and can be ordered through the AC&C Distribution Division
(800-638-8972). If you have any further comments or questions about our charts
or publications, or just want to find out more information about them, see our
Frequently Asked Questions (FAQ) page on our website. Our website URL is
http://acc.nos.noaa.gov/. Use the e-mail address/link at the bottom of the FAQ
page to comment or ask a question."