Geographic Information Systems: An Introduction, 3rd Edition

11.12 Probable Sources of Error

Error is inevitable in all measurements, either quantitative or qualitative, and may range from the serious to the negligible. Yet neither error occurrence nor magnitude can be known in advance. Errors and omissions degrade the accuracy of georeferencing, attribute data, logical consistency, linking, coverage and resolution, and timeliness.

Error may be introduced in any phase of data processing. The following conditions (adapted from Burrough 1986) may affect data quality.

1. Original error sources independent of GIS processing
   1. All surveys and field registrations. Errors may be ascribed to:
      • Instrument inaccuracies
      • Satellite sensor systems
      • Aerial cameras
      • GPS
      • Surveying instruments
      • Various instruments for measuring attribute values
   2. Data processing, as when producing maps used as GIS sources. Errors may be ascribed to:
      • Mapmaking
      • Errors in computations and geodetic networks
      • Mapping instrument inaccuracy
      • Map drawing inaccuracies
      • Data editing
      • Computations
      • Enlarging/reducing and redrawing
   3. Errors due to changes in the field:
      • Registered objects change character
      • New phenomena arise
   4. Errors introduced due to lack of coverage or resolution
2. Errors introduced in GIS data processing
   • 5. Errors in data entry:
     • Inaccuracy in digitization
     • Equipment error
     • Operator error
     • Inaccuracies in entering attribute data
     • Human error (lack of verification routines)
   • 6. Errors in storing data:
     • Insufficient computer numerical precision
     • Storage medium errors
   • 7. Errors ...