Figure 1-7 Contours
The basic contour interval is found in the chart legend and indicates distance between lines. In
Figure 1-7, the basic contour interval is 1000 feet. In addition, intermediate, and auxiliary
contours may be indicated in the legend. Basic, intermediate, and auxiliary contour intervals will
vary depending on the scale of the chart.
Spot elevations are the heights of particular points of terrain above an established datum (usually
Maximum Elevation Figures (MEF) are computed by the National Imagery and Mapping Agency
(NIMA) and take into account both terrain and obstacles.
If the highest feature within a latitude/longitude grid is terrain, NIMA adds 200 feet to the terrain
elevation, plus the vertical accuracy of the identified point. This value is then rounded to the
next 100-foot value.
If the highest vertical obstruction (man-made) is higher than the highest terrain elevation plus
200 feet, then the MEF is computed using the elevation of the obstruction plus its vertical
accuracy, then rounded to the next higher 100-foot value.
What is critical to keep in mind is that the MEF may give over 200 feet or less than 50 feet of
clearance, and does not ensure absolute clearance of terrain or obstacles.
(Information above is collected from DMAAC (MC) SOP 8440.2, 1 DEC 1989)
For Example: 31 means the highest feature within that grid is between 2901 and 3000 feet.
The location of this highest feature within the grid is not identified on the chart, which means
flight planned course may be up to 30 NM from this obstruction. The MEF is used as guidance
for emergency situations on low-level routes.
CHART LEGEND REVIEW