16 Conclusion
16.1 Many users of GIS assume that the spatial data contained and portrayed in their system is absolute and error free. They further assume that the positional information relating to geographic phenomena is precise and accurate. As has been demonstrated in this report, this is not the case. Error and uncertainty are inherent in spatial data.
16.2 There are numerous factors that affect the positional accuracy and reliability of spatial data and contribute to its uncertainty. Many of these factors have been briefly described in this report. That is, the nature of spatial data and how it is conceptualised, how it is modeled, located in space, captured and manipulated, as well as computing and human factors. Positional error is but one of a number of potential sources of error that need to be considered.
16.3 As was described by Maguire et al. “…geography is infinitely complex and must be generalised, approximated or abstracted in order to be represented within the finite dimensions of a discrete computing device.” (Maguire, Goodchild and Rhind, 1991, p112).
16.4 Much of the spatial data in use by organisations today has been captured over many years, by people with varying degrees of competence and conscientiousness, using different software and procedures. It is rare that an organisation will have a good understanding of all of the processes that their data has undergone. As such the quality of this data is unknown. The decisions made based on some manipulation of this data, on the assumption that the data is error free, are also suspect.
16.5 As Chrisman states, (1991, p166) ”… error must not be treated as a potentially embarrassing inconvenience, because error provides a critical component in judging fitness for use. Understanding the error in spatial databases is necessary to ensure appropriate application of GIS…”.
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