Projections Of The Globe Onto A Cylinder example essay topic

Cartography is described by Webster's as the art of making maps, but how is it done? A cartographer doesn't just sit down and draw a map free hand. He has to have techniques and equipment to do the job right and accurately. Maps can be made in three different ways: cylindrical projection, conic projection, and azimuthal projection. These different ways vary the quality and the accuracy of the map. No matter how a map is made it is going to have geographic grids, which help us find and describe locations.

These grids are affected in different ways by each of the projection methods. Cylindrical projections are the projections of the globe onto a cylinder. The easiest way to understand cylindrical projection is to imagine a paper cylinder wrapped around an illuminated globe. The lines from the globe are then projected onto the cylinder in shadows and can be traced. When that is finished the cylinder is slit and unrolled. The problem with cylindrical projection is that there are very few lines that are free of distortion.

The lines that are closest to the part of the cylinder that touched the globe are going to be more accurate, while the ones farther out are less accurate. This makes countries like Greenland look humongous on a map, while making America look smaller then actual size. Conic projections are the projections of a globe onto a cone. The best way to visualize conic projections is to imagine a paper cone with its open end resting over part of an illuminated globe.

The lines are put onto the cone the same way they were put onto the cylinder in cylindrical projection. Then the cone is slit and unrolled. If the cone was directly over the north (or south) pole, the meridians are projected as strait lines radiating straight from the pole, while the parallels appear as portions of the circle. Just as in cylindrical projection, only a few lines, the lines that exist at the points where the cone touches the globe, are free from distortion. Conic projections are commonly used to map middle latitude areas with huge east to west dimensions. To make the maps more accurate, some conic projections use slices from several cones.

The last well-known process for map making is azimuthal projection. Azmuthal projections are the projection of a globe onto a plane. To understand azmuthal projections, imagine a piece of paper touching an illuminated globe at one spot. The lines from a globe are projected onto a sheet and traced. The only distortion free spot on an azmuthal projection is the spot where the plane touches the globe. Common uses of this method are for mapping compact areas of the earth, such as the polar regions.

There are other types of projections, such as the equal-area oval projection. These don't have hardly any distortion at the equator, but they get less accurate the farther north or south you go of the equator. These can be made more accurate, but cutting the oval in the several arching shapes. Cartographers need information from experts in many other fields to make their maps accurate. Map making follows four basic steps: (1) Observation and measurement; (2) Planning and design; (3) Drawing and reproduction; (4) Revision. At the observation level many different collect information for the cartographers.

The geodesist provides an accurate measurement of the Earths size and shape. A surveyor works out the measurements of a place by taking measurements of distance, angles, and elevations. Other experts provide information to the cartographer such as geographers, geologists, and meteorologists. This type of cartography is called compilation mapping, because they are compiling information from different sources to make a map. After compiling the information the cartographer moves on to the planning stage. Here he decides what his map is going to used for, and what the best projection would be for that purpose.

He must also design or pick suitable symbols to put on the map to show landmarks. The cartographer then moves on to the drawing stage. In this stage the cartographer will draw the map out using plastic drafting film, scribe the map by using special tools to cut off the coating of a clear plastic sheet, or they will use computers to make the maps for them. Cartographers often supervise the reproduction of their maps so they know the right color and symbol are being put on the map.

In the revision stage, all the cartographer does is revises his maps to keep them up to date with the changes in the land or scenery. When doing this the cartographer doesn't have to completely redraw the map, he just has to edit certain parts of it. Cartography seems to be more of an art then a science, because you have to have a passion to go into the field before you jump into it. With out that passion your maps could be off, your lines not strait, or many other things could go wrong.