LOW-LEVEL AND TACTICAL FORMATION
read directly from the graphic scale on the chart. The distance between parallels of latitude also
60 NM, and 1 minute of latitude equals 1 NM.
Types. The charts we are most concerned with are the Operational Navigational Chart (ONC -
1:1,000,000 scale), Tactical Pilotage Chart (TPC-1:500,000 scale), and Joint Operations Graphic
Chart (JOG-1:250,000 scale). The ONC is used for high altitude long distance missions; the
TPC and JOG are used for low altitude VFR navigation.
Chart Symbols. Charts have standard symbols for easy identification of information. While
these symbols may vary slightly between charts, the variation is slight and once the basic symbol
is understood, all symbols are easy to identify. The chart legend explains the meaning of the
relief culture, hydrography, vegetation, and aeronautical symbols (Figure C-2).
Relief. Chart relief shows the differences in elevation of the land surface. These include
features such as mountains, hills, plateaus, plains, depressions, etc. Standard symbol and
shading techniques are used in relief portrayal on charts. These include contours, variations in
tint, shading to represent shadow, and spot elevations.
Contour Lines. These are lines connecting points of equal elevation. Figure C-3 shows
the relationship between contour lines and terrain. Notice that on steep slopes the contour lines
are close together; on gentle slopes they are farther apart. The interval of the contour lines
usually depends on the scale of the chart and the terrain depicted. In the illustration, the contour
interval is 1000 feet. Depression contours are regular contour lines with spurs or ticks added on
the downslope side. The ONC shows basic contour lines at 1000 feet while the TPC and JOG
show basic contour lines at 500 feet and 100 feet, respectively. Some of these charts
occasionally have contour lines at other heights so you will need to check each time you use.
Gradient (or Elevation) Tints. The relief indicated by contours is also emphasized on
charts by a system of gradient times. Different tints designate areas within certain elevation
Shading. Perhaps the most obvious portrayal of relief is supplied by a graduated shading
applied to the "southeastern" side of elevated terrain and the "northwestern" side of depressions.
This shading simulated the shadows cast by elevated features, lending a sharply defined, three-
NAVIGATIONAL CHARTS C-3