SO432, Geographical Information Systems
Figures and tables
5 @ 12 60 ___________
Total 100 ___________
This is an open book exam. You may use your text book and any notes you have permanently written in it. You may not attach any papers to the book, but you can tab the book.
Read the directions carefully. You have a selection of questions for the definitions and the short answers.
Quality of your answers is important. For full credit you should use correct terminology, and show that you understand the concepts involved.
Answers in red are not complete, but suggest key concepts
Definitions define 10 of the 12 terms with a concise sentence that clearly shows your understanding of the term: Each is worth 4 points.
(a) Bounding Box:
(b) ESRI shape file vector format, 3 separate files
(c) Lossy compression: trades some detail for smaller file size
(d) MLLW: used on nautical charts in the US for vertical reference level
(e) Metadata include examples of what's included or why
(f) Neighborhood operations:
(g) NGA produces maps and charts for the military
(k) Feature Identifier such as TLID: unique identifier that allows going from one table/file to another
(l) World file
The next five pages contain 5 questions, each of which is worth 12 points. You can answer on the page or on the back of one of the pages. For each answer you should clearly show that understand the principles and use appropriate terminology.
Explain the purpose of the markings on the map above, and what they tell you about the map projection used in the map. Where does this projection have the least distortion, and how can you tell?
A complete answer would use the terms Tissot indicatrix, conformal projection, and equal area projection. While not expected to be included in your answer, the map is a Van der Grinten projection.
These three maps show parts of the MGRS. Explain how the MGRS breaks up the world as shown here, and what these patterns indicate about the projection used for each of the three maps and their distortion.
MGRS uses 6x8 degree zones, and 100,000 m squares.
|The top map shows the 6x8 degree zones. They
are all the same width, but the heights get smaller as you approach the
poles. In reality, because a degree of latitude is nearly the
same everywhere, this means that the projection is compressing latitude
approaching the poles. Longitude is being stretched as you approach the
poles, to keep the meridians from converging.
This cannot be a UTM projection, because it is valid only over a 6 degree zone, and would have extreme distortion far from the central meridian. The UTM projection also has converging meridians.
This is a cylindrical equal area projection (not required for answer).
The center map labels the 6x8 degree zones, shows that latitude is being stretched increasing amounts as you move north, the same as longitude.
The map is Mercator. You should probably have been able to recognize it.
This map shows the 100,000 m grid squares which should be equal area, with one 6x8 degree zone and a small portion of its two neighbors. The squares are all nearly the same size, and the meridians converge toward the poles.
This is a UTM projection. You should probably have been able to recognize it.
Is this map raster or vector? How could you tell, and what difference does it make to users of this data? Is the map displayed at a scale that is appropriate for how it was collected?
This map was printed in raster by the printer (or is shown in raster on the computer screen), and when displayed on screen in the GIS had to be converted to raster if it was vector.
Both raster and vector have scales at which they are collected, although vector will probably be more forgiving when shifting scales.
The diagrams above display the same data set in two different formats. Discuss the different approaches to storing this kind of data, and what you would consider to be the key characteristics of each approach. What makes this a GIS data set?
Why does this map have a dashed cross in each of the corners? Explain why military users would care about this, and if it makes a difference to real users or just geodesists and other mapping professionals.