Lab #3: Data Formats & Models

Geog 206: Intro to GIS

Fall 2010

I. Answer the following questions based on Bolstad Chapter 2 and lecture.

1.       A. What is a data model? It is defined as the objects in the spatial database plus the relationship among them. Model in this case is used to describe many things.

B.      Describe the two most commonly used data models.

·         Vector Data Models and it uses discrete elements such as point’s lines and polygons to represent the geometry of real world entities.

·         Raster Data Models and it defines the world as a regular set f cells in a grid pattern. They are spaced in an x and y direction.

2.       What is topology and why is it important?

Topology is the study of geometric properties that do not change when the forms are bent, stretched or undergo similar geometric transformations. It is important because it has great analytical capabilities. In other words they explicitly record the connection of a set of pathways and so it facilitates network analysis. Overlay operations are also improved when using topological vector models. 

3.       What type of data model would be best for representing hillside slope? Justify your answer.

Raster Data Model is the best representation of a hillside because a hillside slope is a continuous spatial feature best represented in this type of data because it simply represents the variations in a changing surface.

         4. Describe the relationship between spatial detail and cell dimension with regard to raster models.

First it important to understand that as the number of cells required to cover a given area increase dramatically as the cells dimensions get smaller. The smaller the cell the greater the spatial detail. The cell dimension affects the spatial precision of the data set and hence the accuracy. A coordinate applies to the entire area covered by the cell so the point is usually defined at the center of the cell. This means that positional accuracy could be no better than once half of the cell size.

5.       What are the four types of attribute data? Give an example of each.

§  Nominal = descriptive/categorical data

ex. Film clips, audio recording, other descriptive information.

§  Ordinal =   ranked/ordered data

ex.  Getting first, second or third place in a race.

§  Interval = ordered data, with absolute differences in magnitude and arbitrary zero

ex.  temperature

§  Ratio =ordered data, with absolute differences in magnitude and absolute zero

ex.  Weight, distance.

6. List two types of vector data file formats.

·         DXf autodesk (.dxf)

·         MIF/MID mapinfo ( .mif, .mid)

7. List two types of raster data file formats.

·         MIF/MID mapinfo ( .mif, .mid)

·         GeoTIFF, workgroup (.TIF, .TFF)

II. Answer the following questions using the data/tutorials supplied in Ormsby

Chapter 4.

8. You can do all of the following in ArcCatalog EXCEPT:

ü  Identify features

b. Copy data

c. Select features

d. View metadata

9. In the Chapter 4 exercises, does the World.mdb geodatabase contain a feature dataset?

                Yes it does.

10. What are the names of the feature classes contained in the World.mdb geodatabase?

                Cities, countries, disapp_ area, word30

11. What data format does the flight_path.lyr layer file reference?

                It has to reference to the flight_ diverge shapefile.

12. What are two ways to add data to an ArcMap document?

                A. From Arc catalog drag the data to Arcmap. Once it’s there you can look at it as a map display and Table of Contents.

                B. Click on the insert menu and click data frame. In addition you can right click a specific layer and click copy, then right click on the new data frame and click past layers.    

13. How many features (records) exist in the dissap_area feature class?

              699 feature records

14. How can you determine this using ArcCatalog?

       Go to metadata in ArcCatalog -> attribute ( click on it and it will tell you the details for the countries).