UNIT 4 - THE RASTER GIS

UNIT 4 - THE RASTER GIS

Compiled with assistance from Dana Tomlin, The Ohio State University


For Information that Supplements the Contents of this Unit:

IDRISI Tutorial (Lorup/Idrisi Project)
Native American Research Information System (NARIS) (AII/U of Oklahoma)
Raster View of the World (Foote and Huebner/Geographer's Craft) -- Both illustrated and described.
Representation and Data Quality (Chrisman/U of Washington)
Scale, Accuracy and Resolution in GIS (B.C. Environment) -- Map and display scale; data accuracy, density, detail, resolution and uncertainty; raster data resolution; GIS analysis; separation of data and annotation; etc.


  • A. THE DATA MODEL
  • B. CREATING A RASTER
  • C. CELL VALUES
  • D. MAP LAYERS
  • E. EXAMPLE ANALYSIS USING A RASTER GIS
  • REFERENCES
  • EXAM AND DISCUSSION QUESTIONS
  • NOTES
  • Although most of the material in this Curriculum is designed to be as independent as possible from specific data models, it is necessary to deal with this basic concept early so that students can start hands-on exercises with a GIS program. Following Unit 5, we return to the more fundamental concepts and do not address specific vector GIS issues until Units 13 and 14. There are other several places these topics could be placed in a course sequence. We have tried to make Units 4 and 5 as independent as possible so that you can move them within the Curriculum relatively easily.

    UNIT 4 - THE RASTER GIS

    Compiled with assistance from Dana Tomlin, The Ohio State University

    A. THE DATA MODEL

    B. CREATING A RASTER

    Cell by cell entry

    Digital data

    C. CELL VALUES

    Types of values

  • if systems allow several types of values, e.g. some layers numeric, some non-numeric, they should warn the user against doing unreasonable operations
  • integer values often act as code numbers, which "point" to names in an associated table or legend
  • One value per cell

    D. MAP LAYERS

    Resolution

    Orientation

    Zones

    Value

    Location

    E. EXAMPLE ANALYSIS USING A RASTER GIS

    Objective

    Procedure

    Result

    Operations used

    REFERENCES

    Star, J.L. and J.E. Estes, 1990. Geographic Information Systems: An Introduction, Prentice Hall, Englewood Cliffs, NJ. An introduction to GIS with a strong raster orientation.

    Further references can be found following Unit 5.

    EXAM AND DISCUSSION QUESTIONS

    1. What types of geographical data fit the raster GIS data model best? What types fit worst?

    2. Review the issues involved in selecting a resolution for a raster GIS project.

    3. What resolutions would be appropriate for the following problems: (a) determining logging areas in a National Forest, (b) finding suitable locations for backcountry campsites, (c) planning subdivisions to take account of noise from an airport?

    4. Review the methods of planning described in Ian McHarg's classic book Design with Nature (1969, Doubleday, New York). In what ways would they (a) benefit and (b) suffer from implementation using raster GIS?

    5. Using the documentation for the raster GIS program you have, determine how that program uses (a) the concept of "zone" as a contiguous group of cells of the same value, and (b) the concept of several groups of cells that all have the same value. Is there any ambiguity in the way your program deals with these two concepts?


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    Last Updated: August 30, 1997.