Monday, June 13, 2011

Four Compactness Measurements used in Dallas City Council Redistricting

Today, 6-30-11, the final plan was presented to the Dallas Redistricting Commission for study.  Find details at
************* Posts below are archived as of 6-30-11 **************
The staff of the Dallas City Council Redistricting office have done a wonderful job of taking the recommendations of the Chairman of the Redistricting Committee, Dr. Ruth Morgan, and others, and forming an impressive system for measuring compactness. The link they provide, click here, to explain these four measurements is required reading if you want to best understand these measurements.  This linked article also lets you know that we are certainly not the first people to struggle with redistricting.  The issues are almost identical everywhere.

Here are graphics to explain the four measurements as simply as possible. Click on any one you may want to see more clearly.

For more details go to the excellent article linked above, and here.

For the "ideal map for compactness," pPlan10, the measurements used in the spreadsheet below were generated by city staff.  I added the averages to the spreadsheet.  In the chart, area is measured in square miles and perimeter is given in miles.

Probably the most valuable single number to summarize compactness will be the average of the four "indexed" scores on the last line for each measurement.  For pPlan10 those numbers are 1.64, 1.29, 1.71 and 1.36.  Their average is 1.50, in the lower right hand corner of the spreadsheet below.  Remember, a score of 1 would mean no improvement was achieved on average with pPlan10.

Following are the compactness measurements provided by city staff: (click on chart to enlarge)

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