Spatial Join Trouble

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05-02-2013 01:33 PM
dylancummings
New Contributor
Hey Guys,

I am trying to join three different layers. I have one layer of my state (Florida), one layer that i created from the Florida layer where i used the dissolve tool to break the state up into several regions, and then i have an excel file that i am working with that has population data. What i need to know is how many regions have a population greater than xyz and a population density of xyz...Now, to do this i joined my spreadsheet of population data to the Florida layer. Then, i took my dissolved layer and put it on top of the Florida/Spreadsheet joined layer. My idea was that if i spatial joined the dissolved layer with the underlying layer it would aggregate the data and tell me the population (since its by county) of all the counties that make up say Region 1 so i can then tell how many people there are in Region 1....well when i added up the population from my spreadsheet of the counties in Region 1 i get like 490,000 people but when i spatial join it says that the population for Region 1 is like 800 something thousand. I have used the quick right-click join you can do in the TOC and i also used the Spatial Join tool in the toolbox and they both yield the same results. Can anybody help because i can't figure it out to save my life right now...
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RichardFairhurst
MVP Honored Contributor
Hey Guys,

I am trying to join three different layers. I have one layer of my state (Florida), one layer that i created from the Florida layer where i used the dissolve tool to break the state up into several regions, and then i have an excel file that i am working with that has population data. What i need to know is how many regions have a population greater than xyz and a population density of xyz...Now, to do this i joined my spreadsheet of population data to the Florida layer. Then, i took my dissolved layer and put it on top of the Florida/Spreadsheet joined layer. My idea was that if i spatial joined the dissolved layer with the underlying layer it would aggregate the data and tell me the population (since its by county) of all the counties that make up say Region 1 so i can then tell how many people there are in Region 1....well when i added up the population from my spreadsheet of the counties in Region 1 i get like 490,000 people but when i spatial join it says that the population for Region 1 is like 800 something thousand. I have used the quick right-click join you can do in the TOC and i also used the Spatial Join tool in the toolbox and they both yield the same results. Can anybody help because i can't figure it out to save my life right now...


You cannot use Spatial Join for Polygon to Polygon matches like this, because every boundary touch will cause a join, even if the interior of the two shapes has no overlap.  Export the centroids of the county's first and then to the method you are attempting.  The points should fall within only one region polygon and when they are summed they should add up to the correct amount.
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