lab 6

National Elevation Dataset

 

The spacial reference : GCS_North_American_1983.

 The angular unit : Degree (0.0174532925199433).

The datum : D_North_American_1983.

 

Extent:

Top : 39.8291666661°;

Left : -105.788888889°;

 Right : -104.969444445°;

Bottom : 39.3838888883°.

3D image

lab 5

Equal Area:

Equidistant:

Conformal:

The map projection gives people the ability to move the image on a sphere surface to a flat surface. That helps people to have a better general view of the image and enables people to collect data easier from the image. I did experienced the significance of map projection in this map projections exercise. However, we need to pay attention that since the curve of the surface has changed, images can never be exactly the same as the original ones. What we can do is just keep one element the same, such as distance or area, and than use one specific method according to that element. In future, we might be able to create a method which can keep two or more elements exactly the same, which must be able to give people more help than present.

Then, I am going to talk about three kinds of map projections, which are equal area, equidistance and conformal projections. First of all, for the equal area projections, I choose Mollweide projection and Gall Orthographfic, which also known as Gall-Peter projection, to be examples. Although both of them are equal area maps, they still have different features. Mollweide is a pseudo-cylindrical map projection, which has accurate proportions in area. On the other hand, Gall-Peter projection is one specialization of a configurable equal-area map projection known as cylindrical equal-area projection. The standard parallels of the Gall–Peters are 45° N and 45° S. 


Secondly, for the equidistance projections, I choose the Plate carree projection, which is an equirectangular projection centered at the equator, and the Azimuthal equidistant projection, whose distances along great circles radiating from centre are conserved. Because those two projections use different method to keep the proportion of distance the same, the exact distance between Washington D.C. and Kabul from two maps are different.


Finally, for the conformal projections, I choose the Mercator projection, whose Rhumb lines are represented by straight segments, and Stereographic projection, in which  any circle of a sphere, great and small, maps to a circle or straight line.

P.S. Information is from Wikipedia.
http://en.wikipedia.org/wiki/Map_projection#Conformal

Lab 4

 

In these two weeks, we learned the basic usage of the ArcGIS software. In order to practice, we did a series of exercises and finally created a group of maps on the topic of the expansion of airport and the effect of its noise. During this process, I learned a lot and had a fun experience.

 

The ArcGIS software has many advantages. It simplifies the process of making a map and increases the accuracy of map. At the same time, the software makes map making, which can only did by professionals in the past time, nowadays, become handleable for non-professionals, such as students. Moreover, the ArcGIS trained our logical thinking ability, since you have to make map steps by steps. It also trained our sense of spatial, so that we can have a better idea of how our word looks like after finish those maps.

 

However, the ArcGIS also has some disadvantages which need to be improved. First of all is the automatic saving function. The ArcGIS has to have the function of automatic saving so that people will not lost their valuable work by accident, since it really takes a long time to finish a good map. The second point is timing. Although it is handleable for normal people, the steps are still so complicated that people can hardly finish the work individually at the first several times.  Moreover, there are so many steps we need to keep repeating, such as adding north arrow, legend and scale bar. I believe the program can be more simplified so that we only need to add those tuffs once for all the maps in the same group.

 

In conclusion, ArcGIS is a great software which helps people to have a better idea about how to create maps, and, at the same time, trained people’s mind. Of course, it also has some disadvantages, but I believe that it can become more powerful after those improvements.