UNIT 7 - DATA INPUT

UNIT 7 - DATA INPUT

Compiled with assistance from Jeffrey L. Star, University of California at Santa Barbara, and Holly Dickinson, SUNY Buffalo

  • A. INTRODUCTION
  • B. DIGITIZERS
  • C. SCANNERS
  • D. CONVERSION FROM OTHER DIGITAL SOURCES
  • E. CRITERIA FOR CHOOSING MODES OF INPUT
  • F. RASTERIZATION AND VECTORIZATION
  • G. INTEGRATING DIFFERENT DATA SOURCES
  • REFERENCES
  • DISCUSSION AND EXAM QUESTIONS
  • NOTES

    This unit examines the common methods of data input. This may be a good time to take a field trip to a local GIS shop to show students the operation of these various devices. If you can't find local examples, the slide set contains some examples of the hardware items described.

    UNIT 7 - DATA INPUT

    Compiled with assistance from Jeffrey L. Star, University of California at Santa Barbara, and Holly Dickinson, SUNY Buffalo

    A. INTRODUCTION

    Modes of data input

    B. DIGITIZERS

    Hardware

    The digitizing operation

    Problems with digitizing maps

    Editing errors from digitizing

    Digitizing costs

    C. SCANNERS

    Video scanner

    Electromechanical scanner

    Requirements for scanning

    D. CONVERSION FROM OTHER DIGITAL SOURCES

    Automated Surveying

    Global Positioning System (GPS)

    E. CRITERIA FOR CHOOSING MODES OF INPUT

    F. RASTERIZATION AND VECTORIZATION

    Rasterization of digitized data

    Vectorization of scanned images

    G. INTEGRATING DIFFERENT DATA SOURCES

    Formats

    Projections

    Scale

    Resampling rasters

    REFERENCES

    Burrough, P.A., 1986. Principles of Geographical Information Systems for Land Resources Assessment, Clarendon, Oxford. Chapter 4 reviews alternative methods of data input and editing for GIS.

    Chrisman, N.R., 1978. "Efficient digitizing through the combination of appropriate hardware and software for error detection and editing," International Journal of Geographical Information Systems 1:265-77. Discusses ways of reducing the data input bottleneck.

    Drummond, J., and M. Bosman, 1989. "A review of low-cost scanners," International Journal of Geographical Information Systems 3:83-97. A good review of current scanning technology.

    Ehlers, M., G. Edwards and Y. Bedard, 1989. "Integration of remote sensing with GIS: a necessary evolution," Photogrammetric Engineering and Remote Sensing 55(11):1619-27. A recent review of the relationship between the two technologies.

    Goodchild, M.F. and B.R. Rizzo, 1987. "Performance evaluation and work-load estimation for geographic information systems," International Journal of Geographical Information Systems 1:67-76. Statistical analysis of costs of scanning.

    Lai, Poh-Chin, 1988. "Resource use in manual digitizing. A case study of the Patuxent basin geographical information system database," International Journal of Geographical Information Systems 2(4):329-46. A detailed analysis of the costs of building a practical database.

    Marble, D.F., J.P. Lauzon, and M. McGranaghan, 1984. "Development of a Conceptual Model of the Manual Digitizing Process," Proceedings of the International Symposium on Spatial Data Handling, Volume 1, August 20- 24, 1984, Zurich Switzerland, Symposium Secretariat, Department of Geography, University of Zurich-Irchel, 8057 Zurich, Switzerland. Conceptual discussion of the digitizing process.

    Peuquet, D. J., 1981. "Cartographic data, part I: the raster-to-vector process," Cartographica 18:34-48.

    Peuquet, D. J., 1981. "An examination of techniques for reformatting digital cartographic data, part II: the vector-to-raster process," Cartographica 18:21-33.

    Peuquet, D. J., and A. R. Boyle, 1984. Raster Scanning, Processing and Plotting of Cartographic Documents, SPAD Systems, Ltd., P.O. Box 571, Williamsville, New York, 14221, U.S.A. A comprehensive discussion of scanning technology.

    Tomlinson, R.F., H.W. Calkins and D.F. Marble, 1976. Computer Handling of Geographical Data, UNESCO Press, Paris. Comparison of input methods and costs of 5 GISs.

    DISCUSSION AND EXAM QUESTIONS

    1. In his book Computers and the Representation of Geographical Data (Wiley, New York, 1987), E.E. Shiryaev argues that maps must be redesigned to be equally readable by humans and computer scanners, and that this would ultimately make scanning much more cost-effective than digitizing. How might this be done, and what advantages would it have?

    2. The cost of digitizing has remained remarkably constant over the past 20 years despite dramatic reductions in computer hardware and software cost. Why is this, and what impact has it had on GIS? Do you predict any change in this situation in the future?

    3. "Digitizing is a suitable activity for convicted criminals." Discuss.

    4. As manager of a GIS operation, you have the task of laying out rules which your staff must follow in digitizing

    complex geographical lines. What instructions would you give them to ensure a reasonable level of accuracy? Assume they will be using point mode digitizing, and that points will be connected by straight lines for analysis and output.

    5. What type of documents are best suited for automatic scanning?

    6. After reading the article by Marble, Lauzon and McGranaghan on the conceptual model of digitizing, describe and explain the importance of map pre-processing.


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