14 FAA Chart Users’ Guide - VFR Terms and Symbols MEF - Natural Terrain Feature or Natural Vertical Obstacle LAND FEATURES - MOUNTAIN PASSES Mountain Pass symbol does not indicate a recommended route or  direction of flight and pass elevation does not indicate a recommended  clearnce altitude. Hazardous flight conditions may exist within and near  mountain passes. Pilots should be aware that while the MEF is based on the best information available to the Specialist, the figures are not  verified by field surveys. Also, users should consult the Aeronautical Information Services website to ensure that your  chart has the latest MEF data available. Example:  Elevation of obstacle top (MSL) 13161 Possible vertical error +100 Obstacle Allowance +200 equals 13461 Raise to the following 100’ level 13500 Maximum Elevation Figure (MEF) 4.  Round the figure up to the next higher hundred- foot level. 2.  Add the possible vertical error of the source to the above figure (100’ or 1/2 the contour interval when interval on  source exceeds 200’).  1.  Determine the elevation of the feature.  When a natural terrain feature or natural vertical obstacle (e.g. a tree) is the highest feature within the quadrangle: 3.  Add a 200’ allowance for uncharted natural or  manmade obstacles. Chart specifications don’t  require the portrayal of obstacles below minimum  height. 