| |
Chart Scale
Information
The scale of a chart refers to a measurement of area, not distance.
A
chart covering a relatively large area is called a small-scale chart and a
chart covering a relatively small area is called a large-scale chart. Scales
may vary from 1: 1,200 for plans to 1: 14,000,000 for world charts.
Normally, the major types of charts fall within the following scales:
Chart Type
Harbor and
Approach
From
To
1:1,000
1:50,000.
Remarks
Used in harbors, anchorage areas,
and the smaller waterways.
Charts used for approaching more
confined waters are called
approach charts.
coast
1:50,000
1:150,000.
Used for inshore navigation, for
entering bays and harbors of
considerable width, and for
navigating large inland waterways.
General and
Sailing
1:150,000
1:6,000,000
Used for coastal navigation
outside outlying reefs and shoals
when the vessel is generally within
sight of land or aids to navigation
and its course can be directed by
piloting techniques.
Understanding
The size of the area portrayed by a chart varies extensively according to
Chart Scales
the scale of the chart. The larger the scale, the smaller the area
represented.
It follows then that large-scale charts show areas in greater
detail. Many features that appear on a large-scale chart do not, in fact,
show up at all on a small-scale chart of the same area.
The scale to which a chart is drawn usually appears under its title in one
of two ways: 1:25,000 or 1/25,000. These figures mean that an actual
feature is 25,000 times larger than its representation on the chart.
Expressed another way, an inch, foot, yard, or any unit on the chart
means 25,000 inches, feet, or yards on Earth’s surface.
The larger the figure indicating the proportion of the scale, the
smaller the scale of the chart. A chart with a scale of 1:25,000 is on a
much larger scale, for instance, than one whose scale is 1:4,500,000.
1-16
|
