u45-ACCURACY OF SPATIAL DATABASES

u45-ACCURACY OF SPATIAL DATABASES - UNIT 45 - ACCURACY OF...

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Sheet1 Page 1 UNIT 45 - ACCURACY OF SPATIAL DATABASES <toc.html#UNIT45> UNIT 45 - ACCURACY OF SPATIAL DATABASES Compiled with assistance from Nicholas R. Chrisman, University of Washington and Matt McGranaghan, University of Hawaii * A. INTRODUCTION <#SEC45.1> * B. DEFINITIONS <#SEC45.2> o Accuracy <#SEC45.2.1> o Precision <#SEC45.2.2> o Components of data quality <#SEC45.2.3> * B. POSITIONAL ACCURACY <#SEC45.3> o How to test positional accuracy? <#SEC45.3.1> * C. ATTRIBUTE ACCURACY <#SEC45.4> o How to test attribute accuracy? <#SEC45.4.1> o How to summarize the matrix? <#SEC45.4.2> * E. LOGICAL CONSISTENCY <#SEC45.5> * F. COMPLETENESS <#SEC45.6> * G. LINEAGE <#SEC45.7> * H. ERROR IN DATABASE CREATION <#SEC45.8> o Positional measurement error <#SEC45.8.1> o Attribute errors <#SEC45.8.2> o Compilation errors <#SEC45.8.3> o Processing errors <#SEC45.8.4> * I. DATA QUALITY REPORTS <#SEC45.9> o USGS <#SEC45.9.1> o British Ordnance Survey <#SEC45.9.2> o US National standards <#SEC45.9.3> * REFERENCES <#SEC45.10> * DISCUSSION AND EXAM QUESTIONS <#SEC45.11> * NOTES <#SEC45.12> UNIT 45 - ACCURACY OF SPATIAL DATABASES Compiled with assistance from Nicholas R. Chrisman, University of Washington and Matt McGranaghan, University of Hawaii
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Sheet1 Page 2 A. INTRODUCTION <#OUT45.1> * the course thus far has looked at technical issues in: o georeferencing, i.e. describing locations o data structures - how to create digital representations of spatial data o algorithms - how to process these digital representations to generate useful results * among other technical issues in GIS, accuracy is perhaps the most important - it covers concerns for data quality, error, uncertainty, scale, resolution and precision in spatial data and affects the ways in which it can be used and interpreted * all spatial data is inaccurate to some degree but it is generally represented in the computer to high precision * need to consider: o how well do these digital structures represent the real world? o how well do algorithms compute the true values of products? B. DEFINITIONS <#OUT45.2> Accuracy <#OUT45.2.1> * defined as the closeness of results, computations or estimates to true values (or values accepted to be true) o since spatial data is usually a generalization of the real world, it is often difficult to identify a true value, and we work instead with values which are accepted to be true + e.g., in measuring the accuracy of a contour in a digital database, we compare to the contour as drawn on the source map, since the contour does not exist as a real line on the surface of the earth * the accuracy of the database may have little relationship to the accuracy of products computed from the database o e.g. the accuracy of a slope, aspect or watershed computed from a DEM is not easily related to the accuracy of the elevations in the DEM itself Precision <#OUT45.2.2> * defined as the number of decimal places or significant digits in a measurement o precision is not the same as accuracy - a large number of
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This note was uploaded on 10/05/2010 for the course GEO 591 taught by Professor Davidm.mark during the Fall '10 term at SUNY Buffalo.

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u45-ACCURACY OF SPATIAL DATABASES - UNIT 45 - ACCURACY OF...

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