Data quality issues

Data quality issues

1. Accuracy

   • the degree to which information on a map or in a digital database is true
   • Horizontal and vertical
   • attribute
   • conceptual
   • logical
   • affected by:
     • quality of data
     • No. of errors contained in the geodatabase

2. precision

   • level of measurement and exactness of data collected
   • difficult to procure
   • doesn't necessarily mean it's accurate

3. error

   • the imprecision and inaccuracies of data
   • Positional
   • attribute
   • conceptual
   • logical
   • obvious sources
     • age of data
     • aerial cover
     • map scale
     • density of obs
     • relevance
     • vector/raster
     • cost
     • accessibility
   • natural variations of from original measurements
     • positional-coastline
     • accuracy of content
     • sources of variation
       • equipment
       • natural fluctuations
   • Processing
     • numerical
     • topological
     • classification and generalisation
     • digitizing and geocoding

4. propogation

   • where one error leads to another

5. cascading

   • an error in a layer is carried over into a new layer
   • overlay

6. Managed by...

   • sensitivity analysis
     • theoretical modelling of data
     • nominal and ordinal
     • can be used to test precision and accuracy
     • can determine if the datasets are complete to carry the required analysis
   • Implementing industry standards
     • criteria
     • checks
     • training to standards
   • documenting procedures
     • information about the project
   • Measuring and testing products
     • checking against reality
     • para and non-para testing
   • report results in terms of the uncertainties of the data
     • report
       • confidence

7. bias

   • consistent errors in a dataset
   • faulty equipment or poor reading

8. error in rasterization

   • topological errors
   • loss of small polygons
   • effect of grid orientation
   • grid origin and datum