Distribute Demographic data from polygons to points proportionally

SarahWright

Hi, I have demographic data by block group polygons and voter data points. I would like to populate attribute fields in the voter data from the block groups by proportion of the demographics. Example would be if the block group population within's race is 20% other I would like to select 20% of the points and populate the ethnicity field to be other. I have been researching to see if there is a tool that can do this or something similar. Any insight on this is appreciated.

Charlie_Frye

Here is a short geoprocessing workflow (for ArcGIS Pro or ArcMap):

1. Use Identity tool to assign the Block Group IDs to each voter point. 

2. Use Summary Statistics tool to summarize voter points by Block Group ID to get the sum of voters - you may want to select a subset of voters by party or another attribute first, e.g., select republicans and do a summary, then select democrats and do a summary, and so on. You may also need to Add a short integer field to the Voters feature class and Calculate it to have a value of 1. The idea is to produce a summary where you get the sum (count of voter points) within each block group by voter category.  

3. Use the Join Field tool to join the result of each summary to the block group polygons - now the voter counts in the same attribute table as the total population and other demographic cohorts for each block group.

4. Query for block groups with voter counts (by category) that exceed desired proportions of demographic variables, e.g., (!Democrats_SUM!/!TotalPop_CY!) > 0.5

This can all be saved and automated as a geoprocessing model and run as needed on different elections or different geographic areas. 

Depending on how the voter points have been assigned their location in space, i.e., randomly within a voting precinct, or by geocoding the voter's address, it may be moderately to severely unethical to randomly assign demographic characteristics to those points. 

These are two independently compiled datasets. From this data there is no way to know how many democrats are actually over the age of 55, are male or female, or earn over 50,000 per year.  

Instead, one can say is of 59 block groups, 36 have a majority of democrats, and 23 a majority of republicans.  Of the 36 democratic block groups, 28 have a median household income of greater than $80,000 per year, and 22 have a median age over 55. To quickly come up with relevant statements like that, first find the total percentages of relevant demographics for the entire area.  Then see if the voter categories contain strong deviations from those percentages.