HOME ENV510 Landscape Ecology and GIS

Definitions & descriptions | Concepts & issues | Setting up GIS | Using GIS | Applications
Representation | Spatial data | Referencing | Data issues | Accuracy | Error | Sources | Types | Managing | Management

Sources of error

Collection
Input
Storage
Manipulation
Output
Use of results

The main sources of error encountered in a GIS are from:

Collection

• Errors are inherent in the source materials
  
  
• Errors come from field data collection
  
  
• Errors in the analysis of remotely sensed data

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Input

• Inaccuracies come from the data input devices used eg digitising errors
  
  
• Inaccuracies are also inherent in the features being mapped such as boundaries are often not clear cut
  

Storage

• Insufficient numerical precision
  
  
• Insufficient spatial precision

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Manipulation

• Error is propagated as multiple overlay operations are conducted
  
  
• Errors arise from the representation of boundaries - the more convoluted the boundary the more scope for inaccuracies associated with mismatching when overlays are performed
  
  
• Inaccuracy is inherent in the way that classes are defined - many continuous features such as vegetation are mapped as homogeneous with sharp boundaries when really they grade into one another
  
  
• Choice of analysis model
  
  
• Misuse of logic
  
  
• Error propagation
  
  

Output

• Error can be introduced at the plotting phase
  
  
• Error caused by inaccuracy of the output device
  
  
• Error caused by instability of the paper or other medium on which output is printed
  
  
• Scaling inaccuracies
  

Use of results

• Error is introduced when reports generated by a GIS are inappropriately or incorrectly used
  
  
• Information can be incorrectly understood or misinterpreted

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Do this - Finding the error source - Why?

Classify each of the following errors according to the sources identified above.

1. Two data layers overlayed on one another in the GIS with boundary feature that are common to both that are mis-aligned and don't sit perfectly on top of each other

2. a GIS map with no legend

3. a numerical attribute that has been rounded up too much for the detail required in analysis

4. a mis-labelled land cover parcel

5. a property boundary that is in the wrong location a mis-classified pixel

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