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Build Balanced Zones - number of zones "was not reached"

Question asked by Andy.Morgan@arlingtontx.gov_arlingtontx on Nov 12, 2019
Latest reply on Nov 18, 2019 by szelonis_mcpd

I realize this tool is fairly new, but after reading about it and running many times using different criteria it seems like the output is different than what I expected. In particular, the resulting number of zones isn't matching my requested value.


"Number_of_zones" is defined as "The number of zones that will be created", so I understood this to mean the tool distributes my input points as evenly as possible, though certainly not perfectly, into the requested total number of zones. The emphasis here is the zone count which I assumed was the primary guiding factor.


I'm choosing "Number of zones" for the creation method; "60" for number of zones to be created; various combinations of "Compactness" checked/unchecked and using a layer in Distance to Consider; population size / number of generations have ranged anywhere from 70 / 30 up to 5,000 / 1,500. Mutation factor is usually 0.1, though I've gone as high as 0.9. No attribute criteria is used.


The output is always either 57 or 58 zones, never 60 as I requested. Attached is a visual of the raw input, and below is a typical result showing the constraints.


The only way to get 60 is to over-request. For example if I put 62 or 63 for number of zones to be created, depending on the criteria, it then will produce 60 zones if I've guessed correctly. It must be the spatial arrangement that is too challenging for the tool to meet the request. Any tips for me or the next person who encounters this scenario? The documentation says "zone selection criteria should be considered preferences." Is total number of zones part of the selection criteria?



Running script BuildBalancedZones...
Random Seed: 87162
Population Size: 5000
Number of Generations: 1500
Mutation Factor: 0.1
----------------------- Summary Constraints ------------------------
Variable Constraint Type Mean Root Mean Square Error
Number of Features Count 42.621 2.697
Compactness Characteristic 0.883 0.130
WARNING 110269: The Number of Zones requested was not reached
Completed script Build Balanced Zones...