Spatial join: intersect or contains

[DianaGrill]

I am attempting to do a spatial join of 2 polygon layers.  One of a larger geo regions and one of a smaller geo regions. The smaller geo region layer has populations in the attribute layer. Through a join id like to get the population in the larger regions by summing the populatioms of the smaller regions that fall  within them.  Ive tried 2 ways: 1. Doing a spatial join from the larger geo region layer, and getting the sum of all join polygons that intersect it 2. Using the spatial join tool in the toolbox and joining using contains with the large geo regions as a target and the small geo regions as the join (and selecting summingfor the pop field).  The second option gives me smaller numbers.  Which is correct.  

I want each small georegiom to join to one larger region,  but one large georegion will have multiple small georegions.

which is the best join option to use?

thanks!

Diana

[DanPatterson_Retired · Accepted solution]

some possible approaches

http://desktop.arcgis.com/en/arcmap/10.3/manage-data/relationships/deciding-between-relationship-cla...

but joins and relates covers the main issues of choosing between one-to-one or many-to-one questions

[DianaGrill]

Hi Dan,

Thank you so much for your response.  The links were helpful. However, my main question was whether to use' intersect' or 'contains' to define the join.  I want to make sure the populations for my small geo regions are not double or triple counted in joining them to the larger regions. If I use 'contains', will a small geo region just be joined to the large georegion that contains most of its area, or will it possibly also be joined to a large georegion that contains a small amount of its area (2 joins...I don't want this.).  Thank you.

Diana