Weihsenbloggen

Measuring Pottawattamie County, IA Centers

2008-02-09T05:24:00.000-08:00

This link will take you to my site (fledgling) which features a few maps of Pottawattamie County's centers.

http://myweb.unomaha.edu/~bweihs/Centers_Web/index.htm

Feedback is wanted and appreciated.

Centrography Journal Articles

2008-01-26T17:37:00.000-08:00

Here are some articles on centrography, some of which seem to be quite relevant to our discussions either in background or in method.

The Centrographical Method and Regional Analysis
https://myfolder.unomaha.edu/usr/bweihs/public_html/Sviatlovsky_Eells.pdf

Diffusion of Influenza in England and Wales
https://myfolder.unomaha.edu/usr/bweihs/public_html/Hunter_Young.pdf

Centrography in Russian Geography
https://myfolder.unomaha.edu/usr/bweihs/public_html/Poulsen.pdf

Measuring Geographic Concentration by Means of the Standard Deviational
Ellipse
https://myfolder.unomaha.edu/usr/bweihs/public_html/Lefever.pdf

Centrography

2008-01-26T04:36:00.000-08:00

Centrography is “the trend in thought…directed towards the establishment of laws of the distribution of phenomena based on the relationships and migrations of their centers of gravity” (Poulsen, 1959). Measures of center are geographical techniques for locating the position of a point (or area) that represents the average location of the entire population sampled. This population is applicable to a host of variables including (but not limited to) species populations, manufacturing, natural resources, epidemics, agriculture, education, etc. According to Sviatlovsky (1937), to accurately compute these centers “it is necessary to divide a region into sections small enough to constitute a basis for a relatively precise evaluation of the features involved”. In the case of finding the mean center of area in the U.S., counties (or smaller divisions) would be an appropriate unit of area for use in measures of center calculations.
Mean center calculations are very useful, however they are not all there is to measures of center. Other measures include the median point calculation, quartilides, decilides and centrilides. The median point method involves finding “the point of intersection of two orthogonal lines each of which divides the population into two equal groups” (Sviatlovsky, 1937). One major downside to the median point method is that its results may vary radically with small changes to populations because it does not have what Sviatlovsky calls a “sensitive center”. This lack of a sensitive center causes the median point to shift erratically with certain changes to the population, whereas, the mean center will not. This occurs because the median center is calculated based on the position of orthogonal lines, not a statistical operation like the mean center calculation. When populations move only slight distances (over an orthogonal), they can cause major shifts in the median point location. The opposite is true when a large population migrates but does not pass over an orthogonal. Quartilides, decilides and centrilides are similar to the median point method in that they involve lines that divide the population into equal portions, however, the number of dividing lines is higher. This produces divisions of populations in quarters, tenths and hundredths. According to Sviatlovsky, this method is advantageous in regional analysis because it allows for “a greater degree of refinement…than ordinarily profitable”.
Other methods of centrographic analysis (which were not covered) include;
Differntial Centers
Density Profiles
Ellipses of Inertia
Centers of National Economy

My Esri Training

2008-01-19T16:07:00.000-08:00

Virtual Campus Training

Basics of the Geodatabase Data Model
Nov 21 2006

Creating and Editing Geodatabase Features with ArcGIS 9.0-9.1 (for ArcEditor and ArcInfo)
Mar 05 2007

Creating and Editing Geodatabase Topology with ArcGIS 9.0-9.1 (for ArcEditor and ArcInfo)
Jan 13 2007

Creating, Editing, and Managing Geodatabases for ArcGIS Desktop (for ArcGIS 9.0-9.1)
Jan 12 2007

Customizing ArcGIS Desktop (for ArcGIS 9.0-9.1)
Mar 04 2007

Introduction to ArcScan for ArcGIS
Oct 17 2006

Learning ArcGIS Desktop (for ArcGIS 9.0-9.1)
Aug 26 2006

Learning ArcGIS Spatial Analyst (for ArcGIS Spatial Analyst 9.0-9.1)
Mar 04 2007

Understanding GIS Queries
Feb 25 2007

Understanding Map Projections and Coordinate Systems
Sep 09 2006

Advanced Cartographic Methods

2008-01-19T15:59:00.000-08:00

Mic Check 1 2