2 Introduction
2.1 On the surface, the question “Why do my geographic phenomena plot out on the wrong side of the road?” appears to have a simple and straightforward answer. Unfortunately, this is not the case. The question touches on an area of spatial information management that is often ignored by GIS users due to the complexity of the issues that are raised. That is, an understanding of the issues relating to the nature of positional accuracy, error and uncertainty as applied to spatial data.
2.2 Most studies on spatial data error are still at the research level (Burrough and McDonnell, 1998, p220). There are however, some good introductory readings that provide an understanding of the issues involved. One in particular that is often referred to by authors is Burrough (1990). This book, and the relevant chapters have recently been revised (see Burrough and McDonnell, 1998).
2.3 There are many components to error in spatial data, e.g. positional accuracy, attribute accuracy, lineage, logical consistency, completeness and temporal accuracy (Heuvelink, 1998, p6). This report will only explore the nature of positional accuracy, error and uncertainty in relation to spatial data. The issues that will be covered include:
2.3.1 The nature of spatial data and its portrayal in a GIS and on a map.
2.3.2 How is spatial data modeled in a GIS?
2.3.3 How is spatial data located in coordinate space?
2.3.4 How is spatial data captured?
2.3.5 How is spatial data manipulated?
2.3.6 Computing factors that affect spatial data.
2.3.7 Human factors that affect spatial data.
2.3.8 How is the positional accuracy of spatial data measured?
2.3.9 Metadata.
2.3.10 Error in spatial data.
2.3.11 Living with uncertainty in spatial data.
2.3.12 Legal Liability.
2.4 As the issues are complex, an attempt will be made to provide the reader with an introduction to the issues involved. Should the reader wish to explore a particular issue in more depth, references are included for additional reading.
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