Spatial joins in ArcMap (points to polygons) - capturing points that are just outside of outer boundaries

Question

I am working with geocoded crime event data, and attempting to join that point layer with a census block group layer in order to get a count for each census block group (and ideally sums/averages for a couple other variables, but one thing at a time).

When I run the join in ArcMap using the Spatial Join tool (one to one, using the intersect function, no radius), I'm (understandably) unable to capture points that fall just outside of the outer boundary of my block group layer (equates to 2,705 of 1,346,047 events that are not captured). Since ideally I would like to count these data points, I've played around with changing the radius while still using the intersect function. I'm able to then capture these outer points. However, my total count far exceeds the number of events I have in my data (when I use a 1 m radius, my count captures 1,832,027 points for example), which somehow means I'm over-counting despite still calling for a one-to-one join.

I've also tried using Joins and Relates from my block group layer using both point to polygon options. The "fall inside it" option gives me 1,092,213 points (missing points that fall along the outer AND inner borders) and the point "closest to the polygon" option gives me 1,344,971 points (pretty close to my total number of events, but still not capturing some outer points for some reason).

Any thoughts?

Note: I've verified GCSs and datums are the same for both layers.

Answer 1

Interesting question! Making the assumption that you want each point to join to it's nearest census block (assuming it falls outside the block) then one method would be a two-step process:

1. Use the Near tool from the Analysis toolbox with the points as the input layer and the near features as your census block polygons. This will populate the points with the FID of the nearest polygon (in the NEAR_FID column).
2. Use a standard join to join the points to the polygon with the nearest FID.

A bonus of this method is that it will also populate a NEAR_DIST field which will give you the distance to the nearest feature. In most cases it will be zero, but you should get an idea of which features are further away from the census block boundaries.