Lecture_22_Overlaydb2

Lecture_22_Overlaydb2 - Support routine functions of...

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Support routine functions of government and industry (inventory, update) Routine personal use (navigation) Decision support (where to build new school) “Research”
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GIS functions are used individually or in sequence to address questions. Many (most?) questions that really matter, however, are called “wicked”, ill- structured.
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Buffering is the process of defining a zone of influence around a point, line, area or volume. Usually a “fixed” or “crisp” geometry is used. Overlay refers to the combination of different types of data based on a layering metaphor. Nonsense results are easy to obtain.
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Usually based on (created from) features (pts, lines, areas) that already exist in a GIS database. Often zones that result from buffer operations are used to produce a report about what is contained within them. The fixed geometry of most software implementations of buffer analysis is typcially a very simplified view of reality.
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Buffers
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+ 1
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Circular buffer based on an existing point… Find all Find all gidgets gidgets within 5 within 5 km of km of X X . .
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This circular buffer operation is often used as a “clip” operation- e.g., part of the road network is extracted for further analysis.
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Linear buffers are widely used around hydrographic and transportation features.
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In this case a logging company is analyzing timber reserves with respect to their location– proximity to logging roads. This could, e.g., feed into a profit maximizing analysis.
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When lines are close together, linear buffers can exhaust a considerable portion of 2D space… There is often no provision for “counting” n of buffers.
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Laws explicitly restrict certain activities in proximity to schools. Tobacco adverts in this case.
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Combining an orthophoto with buffers to ID location of advertisements Is this building w/in 500’?
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Euclidean (crow flies)– often used, often inappropriately Manhattan (taxicab geometry) Network (road distance) Other (e.g., time, effort)
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Wrong metric? Why Euclidean? Is Manhattan more appropriate?
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They treat space as uniform when we know it is not. For example: Wind has a prevailing direction
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Euclidean
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Travel time that that considers considers factors factors such as such as speed speed limits and limits and congested congested roads. roads.
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This note was uploaded on 04/01/2012 for the course 044 005 taught by Professor Davidbennett during the Fall '11 term at University of Iowa.

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Lecture_22_Overlaydb2 - Support routine functions of...

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