GGS-311_-_Lecture8(3)

GGS-311_-_Lecture8(3) - Accuracy & Uncertainty Matt...

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Matt Rice GGS 311 - GMU Fall 2011
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National Map Accuracy Standards Published by USGS http://egsc.usgs.gov/isb/pubs/factsheets/fs17199.html#US% 20National Horizontal accuracy For maps on publication
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National Map Accuracy Standards Published by USGS http://egsc.usgs.gov/isb/pubs/factsheets/fs17199.html#US% 20National Vertical accuracy Vertical accuracy, as
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National Map Accuracy Standards Published by USGS http://egsc.usgs.gov/isb/pubs/factsheets/fs17199.html#US% 20National Conforming Maps: “This map complies with
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Longley et al. Chp. 6 Definitions Conception, measurement and analysis Vagueness, ambiguity, and other problems Statistical models of uncertainty Error propagation Living with uncertainty
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Introduction Imperfect or uncertain reconciliation and GIS Tension between perfection/ideal and reality It is impossible to make a perfect representation of the world, so uncertainty about it is inevitable
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Sources of Uncertainty Measurement error : different observers, measuring instruments Specification error : omitted variables Ambiguity , vagueness and the quality of a GIS representation Uncertainty is a catch-all for ‘incomplete’ representations or ‘quality’ measures
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A conceptual view of uncertainty. The three filters, U1, U2, and U3, distort the way in which the complexity of the real world is conceived, represented, and analyzed in a cumulative way.
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U1: Conceptio n Spatial uncertainty & formulating an approach to a geographic problem: Natural geographic units? “In many cases, there are no natural units of geographic analysis” Analysis involving more than one variable makes the search for a ‘natural unit’ more difficult
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U1: Conception: Vagueness GIS units/zones & vagueness Statistics & vagueness confidence intervals with boundaries or labels Cartography & vagueness visual communication of vague boundaries or labels perception of vagueness, need to categorize data
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A local assemblage of oak trees or part of an ”oak woodland”on Ragged Boys Hill, in the New Forest, UK. The Ordnance Survey map of the area suggests that there are trees beyond the perimeter of the “woodland”
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GGS-311_-_Lecture8(3) - Accuracy & Uncertainty Matt...

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