Nautical Charts. Types of Scales.
The Nautical Charts showing the Earth’s surface or a portion thereof on a plan, in a certain proportion (scale) and with deformations subject to mathematical laws.
Such a chart must meet the following conditions:
1. The quick and easy insertion of the geographical coordinates of a point;
2. The angles on the chart to be equal to those on the surface of the Earth;
3. The rhumb line and the great circle can be drawn by a straight line.
On a chart are shown a lot of elements using abbreviations, symbols, explanatory notes, warnings, namely:
a. The coast line;
b. The seabed topography;
c. The nature of the seabed;
d. Dangers for navigation;
e. Navigation aids;
f. Natural and artificial navigation landmarks;
g. The magnetic declination and magnetic anomalies;
h. The elements of the tide and currents;
i. Places for anchorage;
j. The boundaries of the different regions;
The nautical charts are divided according to the scale in four categories:
1. General charts:
– Drawn at a scale between 1: 500,000 – 1: 5,000,000
– Are represented large oceanic basins and are used for:
· Study of the navigation conditions;
· Preparing the sea passage;
2. Route charts:
– Drawn at a scale between 1: 100,000 – 1: 500,000
– Used for navigation at deep sea or near the coasts;
– On which are represented the most important elements for navigation;
3. Coast charts:
– Drawn at a scale between 1: 50,000 – 1: 75,000;
– Used for navigation close to land, among islands, fjords, straits;
– Drawn at a scale between 1: 5,000 – 1: 25,000;
– Used for operating in ports, roads, gulfs and bays.
For navigation purposes are used the following cartographic projections:
1. Mercator’s projection:
– With Rectangular Canvas;
– And the rhumb line appears as a straight line;
2. Gnomonic projection:
– Used for the navigation on the great circle;
3. stereographic projection:
– Used for navigation in the polar regions.
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