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According to the VNC, the MEF represents the highest feature in each quadrangle. It refers to

  • AIM RAC 5.4 and CAR 602.15(2b) which basically says "lower than 500 AGL (CAR 602.14(2b)) ok, when for aerial application or aerial inspection, photography, ..."
  • AIM AIR 1.5 which is about "Pressure Altitude" which I guess is because the heights are ASL

Now, the sample quadrangle here shows a MEF of 2700'. Looking at that quadrangle, the highest obstacle I would say is the mountain in the very east, north of 50°35' which is 2290' high. I wonder where that difference comes from.

I think that both figures, 2700' MEF and 2290' are ASL. Therefore it can't be the difference between ASL and AGL. It always seems to be ~400' more than the highest feature.

enter image description here

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  • $\begingroup$ Not sure about Canada but In the US the MEF's are set by taking the highest obstacle in the quad, adding 100ft (for man made objects) or 300 feet (for natural obstructions such as trees) then rounding up to the next 100ft. So under US charting rules it would most likely be 2600 ft. Canada must add an extra 100 ft. And remember that obstacles less than a certain height AGL (200 ft in the US) may not be charted, but if they're the highest object they will still affect the MEF. So if there's a 100 ft tree on top of that mountain that would add to the high point. $\endgroup$ – TomMcW Mar 15 '17 at 4:00
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According to Aeronautical Information Circular 26/11 VFR Navigation Charts—Clarification of the Maximum Elevation Figure the

The MEF is calculated by taking the higher value of:

  • the top elevation of the highest obstacle plus the vertical accuracy (variable) of the terrain source data; or
  • the elevation of the highest terrain plus 328 feet plus vertical accuracy of the terrain source data.

So the 2700' could come from 2290' plus 328' rounded up to next hundred feet.

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