Geoscience Reference
In-Depth Information
Think broadly about ideas such as these and interpret them in the context of
tornado activity. One might view them as “hubs” of communication (Campbell
and O'Kelly, 2012) or adopt other interpretive viewpoints. Then, participate
in the accompanying activity that focuses on one aspect of the analysis of
clustering of data using the concepts of mean center and standard devia-
tional ellipse. There are many other topics to consider in association with the
distribution of data in time and space. What matters is to take a thoughtful
approach to the selection of topics offered here and to related ones that are
available elsewhere.
8.2 Ann Arbor, Michigan—Tornado siren infill project *
One way to get information about how effective communication might be
is to listen to concerned members of an educated public. A number of years
ago, the Director of Environment Coordination Services for the City of Ann
Arbor, Matthew Naud, noted that members of the public had been calling
him to say they could not hear the test warnings from the emergency siren
warning network scheduled on Tuesdays. After mechanical testing of equip-
ment and field checking of complaints by municipal staff, the locations of the
callers were mapped in Geographic Information Systems software. Then, it
became a straightforward matter to suggest possible locations to the City, for
their consideration, for two new sirens to fill coverage gaps that the public
had identified. The strategy below outlines the process actually employed in
this data distribution problem. The reader will have other opportunities in the
“Practice” section at the end of this chapter.
8.2.1 Filling gaps in tornado siren coverage: Ann Arbor, MI
Following extensive field work by the City of Ann Arbor, simple location by
street position of existing towers followed by a tessellation by Thiessen poly-
gons of that distribution, offered simultaneous display on a map of the exist-
ing siren locations partitioned according to the proximity to siren. In Figure
8.1 , the red dots show the existing siren location and the heavy red lines
show the Thiessen tessellation of those dots. What the tessellation alone does
not show is how far away any given point, within the Ann Arbor freeway ring,
is from an existing siren.
To get an added visual fix on this concept, concentric ring buffers were intro-
duced around each dot. Successive buffers have radii of 1000, 2000, 3000,
4000, and 5000 feet. This pattern conveys the fact that sound and hearing
* With many thanks and greatest appreciation for input, in the early 2000s, from: Matthew
Naud, Environmental Coordination Services, Director, City of Ann Arbor; Merle Johnson,
Information Technology Services, City of Ann Arbor; Adele El Ayoubi, Neighborhood Watch
Coordinator, City of Ann Arbor Police Department; Karen Hart, Planning Director, City of
Ann Arbor.
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