Some question on Spatial Match and Find nearest tool usage

[LiuZhang]

I recently attempted Challenge #100: Find Ned!, which push me to understand the spatial tools a bit more.

There are quite a few questions I would like to ask now.

As the general solution to the challenge is to build grid then match on the nearest find.

Q1: Find Nearest

As Find Nearest tool doesn't have the option to Return the distance to the nearest edge as Distance tool did, somewhere it is mentioned Find Nearest check the centroids of two spatial objects when they are not points. (See diagram) does that mean, we can have situation where one grid is very close to the line, but far from the center of the line object, then it could be not selected as nearest when compared with a grid that is closer to line centroid.

1 should be closer as perpendicular distance

Q2: Spatial Match

For both Spatial Match and Find Nearest tool, we have Target and Universe input, from the documentation, it is for each Target input, compare with all Universe input. Then used to check intersections, as it is kinda symmetric behavior, therefore it is advised to link the smaller dateset to U? as like warning with Append tool?

Thanks

[danilang · Accepted solution]

Hi @LiuZhang 

Question 1

It is the distance between centroids and not perpendicular distance

allClosest

Question 2(Find Nearest)  

In the Find Nearest tool, the relationship is not symmetrical.  The target is always the group of objects that we're interesting in.  The universe is the possible set of objects that can fulfill the conditions. In our example we are asking the question "Which point is closest to the vertical line?"  The line is the target and the points are the universe.  If we flip the T and U inputs the question becomes "Which line is closest to each of the points?"  You can see this if you switch the inputs getting two records matching since the line is closest to each of the points.     

Question 2(Spatial Match)

The answer here depends on the operation that you're using.   Intersects and Touches are symmetrical operations so the T and U can be swapped, though it's best practice to always connect your target areas to the T.  The other operations, like "Target contains Universe" are not symmetrical so you need to connect the inputs accordingly

Dan     

[LiuZhang]

@danilang Thanks for answering, as most often I play with intersections, so it is always a bit fuzzy regarding to the correct use of T and U. Now I understand it better.