An aeronautical chart is a pictorial representation of a portion of the earth's surface upon which
lines and symbols in a variety of colors represent features that can be seen. In addition to ground
images, many additional symbols and notes are added to indicate additional information
necessary for navigation. Aeronautical charts are vital aids to navigation. Because of their great
importance, you must be thoroughly familiar with the wide variety of aeronautical charts
available to you and their proper use.
Scale. The ratio between any given unit of length on a chart and the true distance it represents
on the earth is the scale of the chart. The scale may be relatively uniform over the whole chart,
or it may vary greatly from one part of the chart to another. The charts you will use will
normally have a uniform scale. Charts are made to various scales for different purposes. If a
chart shows the whole world, it is drawn to a small scale; otherwise it would be too big to be
useful. If a chart needs to show a lot of detail, it needs to be drawn to a large scale. Remember:
"Large area=small scale and small area=large scale" (Figure C-1). The scale of a chart may be
given by a simple statement, such as, "1 inch equals 10 miles." This means 10 miles on the
earth's surface is shown as 1 inch on the chart. On aeronautical charts the scale is indicated as a
representative fraction or graphic scale.
Representative Fraction. The scale may be given as a representative fraction, such as
1:500,000. This means that one of any unit on the chart represents 500,000 of the same unit on
the earth. For example, 1 inch on the chart represents 500,000 inches on the earth. A
representative fraction can be converted into a statement of mile to the inch. Thus, if the scale is
1:1,000,000, 1 inch on the chart stands for 1,000,000 inches or about 68.5 NM. Similarly, if the
scale is 1:500,000, 1 inch on the chart represents about 13.7 NM. Thus, the larger the
denominator of the representative fraction, the smaller the scale.
NAVIGATIONAL CHARTS C-1