MIL-PRF-89201B
3.6 Chart design. Nautical charts rely upon a layered coverage at
different scales to bring a navigator into port. This is because the same
detail cannot be shown on a small scale chart as on a large scale chart.
3.7 Charts in a series. Some charts may be part of a coordinated
series. Charts in a series have a common scale that is computed at the series
midpoint. A coordinated series is identified by the common mid-latitude
stated in the title.
3.8 Size and dimension. Size and dimension of a chart are dependent on
scale and coverage requirements of a given area combined with the availability
of chart compilation data. Chart dimensions are also subject to modification
when attempting to locate a chart's neatlines on exact graduation
subdivisions.
3.9
Projection.
3.9.1 Purpose of projection. A nautical chart represents part of the
spherical earth on a plane surface. Because a sphere cannot be transferred to
a flat surface without distortion, the sphere surface is "projected" onto a
"developable surface". A developable surface is one that can be flattened to
form a plane. This process is known as chart projection. Most NIMA Charts
will be constructed on a Mercator or Transverse Mercator projection.
3.9.2 Projections for use at higher latitudes. As required by the NATO
Standardization Agreement (STANAG) 1113MC (Edition No. 3), "General
Specifications for Projections Required for Nautical Charts for the Polar
Regions and the Higher Latitudes", the type of chart projections that would
normally be used in polar regions and higher latitudes are shown in the
following matrix:
Latitude
1:50,000 or Larger
1:50,001 and smaller
Lower than 80(if chart
Mercator
Mercator
extends above 80, greater
part is below 80)
70 or higher, but does not
Mercator*, Transverse
Polar Stereographic or
cover pole
Mercator or Lambert
Lambert Conformal
Conformal
Higher than 70 and covers
Not Applicable
Polar Stereographic
pole
* Harbor and Approach charts of scales 1:50,000 and larger may be compiled on
a Transverse Mercator projection.
3.9.3 Graticule spacing. Graticule lines cannot be spaced a standard
distance apart, because nautical charts are produced at various scales, and
the length of a degree of longitude varies with latitude. The navigator must
be able to reach from any point on the chart to a graticule line, using his
dividers. Therefore, graticule lines on nautical charts are spaced from about
11.25 cm (4.5 inches) to about 25.0 cm (10 inches) apart. All parallels and
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