topic Re: Empty Output generated from Union operation in Geoprocessing Questions

Empty Output generated from Union operation

JonathanBrown — Fri, 20 Jun 2014 12:43:05 GMT

I am attemption to Union two shapefiles. I made sure both shapefiles have the same defined coordinates before trying to Union and I am still getting and empty output generated warning. I found on google that some people had the same issue and after repairing Geometry it worked for them. That did not work out for me.

Does anyone have any potential solutions on how I can achieve this Union operation successfully or have any insight on why this operation completes but generates an empty output.

My task:

I have two large shapefiles that I was trying to intersect. I was limited by my computational constraints, so I gave it the classic attempt of divide and conquer. I split shapefile 1 into two shapefiles 1a and 1b. Intersected them with Shapefile 2. Now I am trying to Union the two intersects together.

Thanks in advance for any suggestions.

000117 : Warning empty output generated.

Re: Empty Output generated from Union operation

markdenil — Fri, 20 Jun 2014 12:57:56 GMT

One assumes you divided the large shapefile into two non-overlapping geographic areas.
thus, a Merge or Append may be a better option for joining the intersect outputs.

Are there features in each intersect output?

Re: Empty Output generated from Union operation

JonathanBrown — Fri, 20 Jun 2014 13:12:56 GMT

There are features in the intersect outputs that are very much needed.

I posted a simple example of my task.
The original task is that I really have divided shapefile1 into 28 sub shapefiles. These 28 sub shapefiles were intersected with Shapefile2.

then I had a script that takes the Union of shapefile1a and Shapefile1b and creates and output X.
The code will then iterate through the rest of the sub shapefiles and redefining output X ....

pseudo code:

inFeatures = [shapefile1a.shp , shapefile1b]
outfeatures = "X.shp"
arcpy.Union_analysis(inFeatures,outFeatures)

For (i in Range(26) :

inFeatures = [shapefile1c.shp, X]
outFeatures = "X.shp"

and so on for shapefiles1d, shapefile1e etc....

I am quite a novice at arcGIS. Could you please explain why Merge vs Union or Append vs Union will achieve what I am trying to do?

Thanks.

Re: Empty Output generated from Union operation

JonathanBrown — Fri, 20 Jun 2014 13:17:23 GMT

At least for the initial two shape files that are being Unioned, there is a significantly decent size of overlap spatially from what I can see by importing the shapefile1a and shapefile1b.

Re: Empty Output generated from Union operation

markdenil — Mon, 23 Jun 2014 11:23:50 GMT

You managed to 'simplify' your problem into something quite different from your second explanation.
That second explanation may be a bit oversimplified too.
Your pseudo code does not make your workflow much clearer.
This forum is not really a good place to gloss over 'details'.

for example:
Why are you unioning the subfiles of Shapefile1?
Where does Shapefile2 come in?
is outfeatures always "X.shp"?
I assume you realize that there is a difference between outfeatures and outFeatures ?
why does a for loop start up between two union operations?

No one can guess any of this.
Post your real code, and put it between code tags (the '#' button on the editor toolbar).

Be all that as it may...

If you have concerns about geometry issues, I suggest converting the shape files to file geodatabase feature classes
and then running check or repair geometry. Shapefiles can be depressingly tolerant of internal faults.

I assume your output is important, I asked if there was any output from the first stage(s)
(that is, in the "two intersects" you were trying to union, as per your first post).