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| TOOLS OF THE OCEANOGRAPHER: Equipment: Maps |
| A. Maps | |
| 1. Map Projections • Mercator Projection • Polar Projection • Sinusoidal Projection |
2: Orientation |
| 3: Topographic Maps | 4: Hydrographic Maps |
| A working knowledge of basic world geography is essential for understanding world wide oceanographic concepts. Since the Earth is a sphere it is very hard to represent it on a flat piece of paper. Map makers have done this in a variety of ways but each way has its own faults and distortions. The following are examples of the most commonly used map projections: |
| 1. Map Projections |
| Mercator Projection |  |
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| Polar Projection | |
Polar
Projection: The polar projection is constructed by placing a plane tangent
to the globe at one pole. A pin-point light source located at the other
pole projects the representation of the globe on the plane of paper. This
projection is often used in combination with the mercator projection because
it shows a much better representation of the polar regions. |
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| Sinusoidal Projection | |
| May have a single central meridian or several central meridians. Areas on the map are proportional to the same areas on Earth. Distances are correct along all parallels and the central meridian(s). Shapes become increasingly distorted away from the central meridian(s) and near the poles. | |
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| 2. Orientation |
| Orientation: By conventional agreement a map is always oriented in such a way that north is at the top, west to the left, and east to the right of the map. North is shown on the map always as true or geographic north, that is the top of the sphere. It differs from magnetic north as shown by the compass. The difference between geographic and magnetic north is the declination usually shown on a map as the declination diagram. Other features shown in the legend of a map are symbols by which important markers are represented. |
| 3. Topographic Maps |
| Topographic Maps: All the maps described thus far are called planimetric maps; they show the relative position of points but do not indicate their relief (elevation above or below sea level). The three dimensional surface of the land, that is its topography, may be portrayed on a one dimensional piece of paper by use of contours. These contour lines show the intersections of the ground surface with a series of horizontal planes at definite intervals above the datum plane (sea level). |
| 4. Hydrographic Maps |
| Hydrographic Maps: For sea areas, the equivalent of the topographic maps on land areas are termed hydrographic maps. They are mostly prepared by two agencies, the U.S. Coast and Geodetic Survey for coastal areas and the Oceanographic Office of the Navy for open sea areas and foreign lands. Hydrographic maps depict the outlines of water bodies and also show somewhat of the bottom topography of the areas by soundings of which the numerical value is indicated. |
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