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Beyond Metadata: Towards User- Centric Description of Data Quality Michael F. Goodchild University of California Santa Barbara.

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Presentation on theme: "Beyond Metadata: Towards User- Centric Description of Data Quality Michael F. Goodchild University of California Santa Barbara."— Presentation transcript:

1 Beyond Metadata: Towards User- Centric Description of Data Quality Michael F. Goodchild University of California Santa Barbara

2 Metadata n Data about data –handling instructions –catalog entry –fitness for use n What is known about data quality –a measure of the success of spatial data quality research –much progress has been made –FGDC CSDGM 1994 –ISO –DDI –EML

3 Two tests of success n Geobrowsers –Google Earth –geotagging –Wikimapia –Where 2.0

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9 CSDGM, ISO n Do they match the state of research? –early 1990s –SDTS discussions of 1980s –the five-fold way positional accuracy attribute accuracy logical consistency completeness lineage n Do they represent a user perspective? –committees staffed by data producers –production control mechanisms?

10 Producer or user? n Producer-centric –details of the production process: the measurement and compilation systems used –tests of data quality conducted under carefully controlled conditions –formal specifications of data set contents n User-centric –effects of uncertainties on specific uses of the data, from simple queries to complex analyses –simple descriptions of quality that are readily understood by non-expert users –tools to enable the user to determine the effects of quality on results

11 Increasing complexity n Self-documentation –notes to oneself n A colleague –brief description n Another discipline, language, culture –ideal metadata/data ratio?

12 social distance complexity of metadata

13 Seven issues n Areas in which research has moved beyond the standards –Accuracy of Spatial Databases 1989 –Measurements from Maps 1989 –15 books –1000 journal articles

14 1. Decoupling the representative fraction n Ratio of distance on the map to distance on the ground –no flat map of a curved surface can have a constant RF n RF as a surrogate –positional accuracy –spatial resolution –map content n RF undefined for digital data –inherited from source maps –extended by convention aerial photographs (RF of the photographic plate) digital orthoimagery (positional accuracy)

15 2. Accuracy or uncertainty? n Accuracy –a true value z exists –a measured value z* –error z*-z –RMSE –theory of measurement error –error propagation n Uncertainty –vagueness in definitions no truth perhaps a consensus? –lack of replicability n Change of paradigm around 1992 CSDGMISO accuracy857 uncertainty00

16 3. Objects and fields n A fundamental distinction –1992 –appears nowhere in the standards n Discrete object conceptualization –an empty table top –occupied by discrete, countable objects –points, lines, areas, volumes n Continuous field conceptualization –a mapping from location x to value z –a single-valued function of location

17 z'(x) = z(x) + δz(x)

18 Separability n Phenomenon conceptualized as a field –impossible to separate positional and attribute accuracy –interval/ratio (elevation) –nominal (land cover class)

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20 4. Granularity n Metadata definable at any level –individual vertex –point, line, area –layer –geodatabase n Metadata as a form of generalization –economies of scale n Spatial non-stationarity n Multiple lineages

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23 5. Collection-level metadata n Describing the properties of entire collections n The Geospatial One-Stop –www.geodata.gov n There will always be more than one one-stop –how to know where to look?

24 GOS coverage, 1/06

25 6. Spatial dependence n Tobler’s First Law –nearby things are more similar than distant things –applies to errors –relative accuracy almost always better than absolute accuracy –covariances as important as variances

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27 Marginal or joint properties? n Visualization of marginal properties n Analytic functions respond to joint properties –slope –area n Joint properties must be described at a higher level –relative errors of vertex positions –described at level of vertex collection

28 Cross-correlation n How are errors on Layer 1 related to errors on Layer 2? n Error as an issue in interoperability –what happens if I superimpose these layers? n Two layers will almost always not fit –depends on lineage of each –how bad is the misfit? –will it affect my analysis? n Binary metadata –the ability of a pair of data sets to interoperate –not available from either’s unary metadata n If GIS is about overlay –then binary metadata are essential

29 The way forward n Reopen the metadata debate –an unpopular move –it’s hard enough to persuade people to provide metadata –a standard before its time –standards should emerge only after research is complete n It’s our responsibility –the research task does not end with journal publication –metadata standards express the state of our research n Many other issues not related to data quality –possible allies


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