lab5 Projections in ArcGIS

Conformal projection: 

Stereographic projection: the distance from Kabul to Washington D.C is: 9878miles Mercator projection: the distance from Kabul to Washington D.C is: 10112miles





Equidistant projection:

 Two-point equidistant projection: the distance from Kabul to Washington D.C is: 8098miles

 Sinusoidal projection: the distance from Kabul to Washington D.C is: 8098miles

Equal area projection:

Bonne projection: the distance from Kabul to Washington D.C is: 7244miles
Eckert Ⅱ projection:the distance from Kabul to Washington D.C is: 6916miles



Maps were used by people for navigation since a long time. However, after Columbus discovered that the earth is round, people realized that flat maps are not enough and developed Globes. But people use projections on maps again nowadays. Projection of 3D earth on 2D maps is not easy and deformation is also inevitable, because projection can only preserve one property out of distant, area, and shapes & angles. 
Different projections have different functions. Equal area projection preserves the area of earth and can show accurate sizes of landmass. For example, equal area projection is useful in population density and land use, especially in agriculture. Equidistant projection preserves the actual distance from a point or a line, and it is useful for people to calculate distance as we calculate the distance from Washington D.C to Kabul, Afghanistan. The last one, conformal projection, preserves angles and shapes, and is most used for navigation in a local area. 
However, one projection can only offer limited information and distort other properties. If people would like to see the whole earth, they need to combine information from several projections. The most pitfall of projection is that it is country-oriented. For example, in the Mercator projection, Greenland seems like the largest area on the earth, which is really inaccurate and misleading! I guess the reason for the enlarged Greenland area is that the designer of Mercator projection is Flemish, who would like to make his homeland like the center of the world. But maps play an significant role in portraying the world around us, and can easily manipulate our minds. Maybe people in the past used to believe that Europe is the center of world. Another pitfall of projection is that it distorts distance in large scale. When we calculate the distance from Washington D.C to Kabul, Afghanistan, the data varies greatly in different maps. For example, in stereographic projection the distance is 9878miles, while the distance in EckertⅡ projection is only 6919miles. Look at how big the difference is! It is really difficult to complete a large-scale a mission which demands highly precision.

Despite the pitfalls, projection is also really useful in our life as it shows the whole earth on a 2D plane. For example, when people need navigation in a local area, they can use Mercator projection as a guide. And when scientists study the earth structure, they can apply Stereographic projection as a tool. The errors can be minimized if people take some time to choose suitable projections according to their demands. And I hope in the future people can develop better projection to represent the earth and maybe invent a tool to combine all the benefits from each projection.