topic Re: How to troubleshoot a dissolve that returns empty output. in New to GIS Questions

How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Fri, 09 Feb 2018 23:45:00 GMT

I have a map layer containing election district boundaries. All of the election districts are located within towns. As a learning task, I'm attempting to dissolve the boundaries of the constituent districts to create a town shape layer. I have a few statistical fields in the layer that I would like to sum when I dissolve the district boundaries.

I've tried using the Dissolve command, but keep finding it returns an empty table (" WARNING 000117: Warning empty output generated."). I'm also unclear on what to enter in the Output feature class field. By default the field seems to be populated with the name of another shape layer in my project, but I don't want to overwrite that layer.

After reading some forum posts, I thought maybe my geometry was corrupted. I tried the Check Geometry tool, which did return an error (" WARNING 000442: could not find spatial index at -1 in Westchester 2014_Town boundaries"). I also tried the Repair Geometry tool which ran successfully. However, when running the dissolve command I still am getting empty output.

Re: How to troubleshoot a dissolve that returns empty output.

DanPatterson_Retired — Sat, 10 Feb 2018 05:20:06 GMT

Assuming you are using Dissolve in Data Management

Your input parameters are listed as

Dissolve_management (in_features, out_feature_class, {dissolve_field}, {statistics_fields}, {multi_part}, {unsplit_lines})

The first two are your input featureclass and its output (Dissolve has to produce a new file).

The 3rd is asking what field are you using for the dissolve? do you have a field with the Town names? If so, that would be the one. other parameters... read about them since they provide other outputs information and also control how the geometry is treated

Re: How to troubleshoot a dissolve that returns empty output.

DanPatterson_Retired — Sat, 10 Feb 2018 10:52:58 GMT

Shared to Geoprocessing‌

GeoNet Community Structure to get a wider audience

Re: How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Sat, 10 Feb 2018 13:19:30 GMT

Yes, I used Town Names as the aggregation field:

Re: How to troubleshoot a dissolve that returns empty output.

DanPatterson_Retired — Sat, 10 Feb 2018 17:23:47 GMT

good... but what were the warnings? At least it wasn't an error. Are they all text fields? since First seems to be the only option for most.

Re: How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Sat, 10 Feb 2018 19:29:21 GMT

The only warning refers to the empty output: WARNING 000117: Warning empty output generated. I used First for any field that contains geography that would still apply to a town-level shapefile -- like country, state, and county. Since repeatedly re-specifying the Dissolve specs got a bit old, I only added a few of fields that need to be summed this time.

Re: How to troubleshoot a dissolve that returns empty output.

DanPatterson_Retired — Sat, 10 Feb 2018 21:10:20 GMT

Do a query and select a single town as a test (select by attributes)

Export the selection to its own featureclass in a geodatabase on a local machine.

Try a dissolve on that

Your file paths are long and the names with the dots etc are a bit strange

Re: How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Sat, 10 Feb 2018 21:50:18 GMT

The field names with the dots are the result of a join between the shapelayer and a data table. In case it was a memory issue, I retried running the dissolve on just the shapefile but no luck.

Re: How to troubleshoot a dissolve that returns empty output.

DanPatterson_Retired — Sun, 11 Feb 2018 00:37:20 GMT

zip the shapefile... attach it to your question (may have to use the advanced editor option in the top right of the question).

I will check the dissolve.

Also, I wouldn't do a dissolve unless the joins were permanent in any event

Re: How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Sun, 11 Feb 2018 14:00:53 GMT

I've attached the original shapefile that I downloaded from the public website. The 2 leftmost characters from the TWD text field indicate the town. I used that field to create a new field, Town. Then I imported TownNames by joining the shapelayer with a lookup table. I've placed the new shape layer with the 2 new fields in this layer package (which seems to be an exportable entity), and attached that here as well. Before attempting the dissolve, I did run repair geometry which deleted some features with null geometry.

Thanks again for your help.

Re: How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Sun, 11 Feb 2018 14:04:44 GMT

Dan Patterson wrote:
Also, I wouldn't do a dissolve unless the joins were permanent in any event

Dan, what does 'permanent' mean in this case?

Re: How to troubleshoot a dissolve that returns empty output.

DanPatterson_Retired — Sun, 11 Feb 2018 14:26:57 GMT

If you make a join by most methods... they are temporary and can be removed. ie (Add Join tool temporary)

You make permanent joins by using Join Field or by saving the the results of Add Join using several options (ie Copy Tool for instance)

Re: How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Sun, 11 Feb 2018 14:37:22 GMT

If you make a join by most methods... they are temporary and can be removed. ie (Add Join tool temporary)
You make permanent joins by using Join Field or by saving the the results of Add Join using several options (ie Copy Tool for instance)

Of course, that makes perfect sense and also explains why I couldn't remove the redundant fields from the joined table. I'll go back and address that and see if the dissolve works.

Re: How to troubleshoot a dissolve that returns empty output.

KathyKaufman — Sun, 11 Feb 2018 14:56:57 GMT

Dan Patterson‌, you are hero of the month! The temporary join was the problem. Thank you so much!!!!

Re: How to troubleshoot a dissolve that returns empty output.

DanPatterson_Retired — Sun, 11 Feb 2018 17:05:14 GMT

Ahhh thank goodness! Glad it worked out!