SO432, Geographical Information Systems

Exam 1, Fall 2003


Definitions    10 @  3        30   ___________

Short answer    2 @ 10        20   ___________

Figures         2 @ 10        20   ___________

Essay           1 @ 30        30   ___________

Total                        100   ___________


Read the directions carefully.  You have a selection of questions for the definitions and the short answers.

Insure that you devote at least 15 solid minutes on the essay.

Quality of your answers is important.   For full credit your should use correct terminology, and show that you understand the concepts involved.



Definitions:  define 10 of the 12 terms with a concise sentence that clearly shows your understanding of the term:  Each is worth three points. Comments are key points often missed, and not complete answer.


(b)DPI: printers or scanning

(c)Lossy compression: tradeoff

(d)Meades Ranch:

(e)MLLW: chart datum

(f)NGVD 1929 (or NAVD88 in second version): vertical datum

(g) Neighborhood operations e.g. slope or filtering

(h)NIMA for military

(i)Orthometric height:



(l)Tidal epoch: NATIONAL TIDAL DATUM EPOCH (1983-2001).  Previous tidal Epochs were determined for periods 1924-42, 1941-59, and 1960-78.  The (NTDE) is a specific 19-year period over which tide observations are taken to determine Mean Sea Level and other tidal datums such as Mean Lower Low Water and Mean High Water. The NTDE has been adopted so that tidal datum determinations throughout the United States will be based on one specific common reference period.


Diagram showing tidal epochs.

Answer 2 of the following 3 short answer questions.  Each is worth 10 points.


(a)    A NIMA publication lists about 20 ellipsoids used around the world, and over 100 horizontal datums.  What is the difference between an ellipsoid and a datum, and why are there so many more datums than ellipsoids?


Horizontal datum is shape + starting location. 

Geoid not involved in datum or ellipsoid other than fitting the starting location to ellipsoid

Geoid varies by plus or minus 100 meters from ellipsoid.



(b)   What is feature coding, and why do we use it in GIS operations?

Can use variable levels of coding, not just major/minor

(Or in second version)

(c)    How is a relational database set up?

Should use term records/attributes/fields (quick diagram)


(d)   Do nautical charts and land maps define sea level the same way?  Why or why not?

Chart: NTDE based on local tide gauge and MLLW, adjusted every 25 years or so

Map: vertical datum for country/continent, adjusted every 50 years or so, for mean sea level


You must answer this question, worth 10 points.


The diagram below shows two map projections of the same area, with the 100,000 m grid squares of the MGRS shown.

        What is the difference between the two projections?

        Why does the MGRS use letters for the 100,000 m grid squares?


 Mercator Projection


  UTM projection


You must answer this question, worth 10 points.


The figure below shows four map projections.

        Explain what the overlaid circles and ellipses tell you, and how these projections differ.

        Discuss the geometry behind the construction of these four projections.

        Which, if any, of these projections would be good for navigating a tank company in Iraq.  Defend you answer.



Cannot be both conformal and equal area—upper left is only one of the two, but over this region is pretty good on both counts.

Conical, cylindrical, and planar geometry.

Lower left is not UTM, because the projection is not conformal (but is equal area).



Essay.  This is worth 30 points.  You should use correct terms and show that you clearly understand the concepts involved.



The president of Rent-A-Raster Maps, Inc. has just made a presentation to the admiral in charge of NIMA.  A persuasive speaker, he has convinced that admiral that all of NIMA’s mapping needs for the military can be solved with a single GIS data base.  He proposes the following characteristics, which he is prepared to produce for NIMA:

        Worldwide coverage

        Raster data.

        1 m resolution.

        Collected on UTM projection.


Discuss how you would brief the admiral on the merits of this proposal.  Since the admiral is new to the GIS and mapping world, insure that you explain the basic principles behind your recommendation to proceed or not.


Surface area of earth about 5x1014 m2 

kb=103 bytes

MB = 106 bytes

GB = 109 bytes

TB = 1012 bytes


So 512 TB for each raster layer if it only needed 256 possible values


While we need worldwide coverage, does it all have to be 1 m?

What are advantages of raster and vector?

What about UTM zone boundaries, where every war is fought?