Question regarding Dissolve and its "Create multipart features" parameter

Question

Hi community!

I need to backpedal to my dissolve question from earlier (for reference):

I have a table of whale sightings data with dates, group IDs of the whales seen, coordinates, and many other fields. I need to do some analyses on different whale groups looking only at the days present in a geographic region rather than each sighting of a group - some whale groups will split during the day and will be counted as two different sightings, but we only want to count those as one (hopefully that makes sense!).

I tried to use the dissolve tool which ran fine, but the resulting attribute table contains only 3 or 4 of the fields from the original attribute table which has 31 fields. I would like to retain all fields. I've tried the Pairwise dissolve as well with the same result.  How can I accomplish my goal without losing fields?

When running the dissolve tool, I need help visualizing what selecting the multipart features parameter is doing. My original table has 2132 sightings. If I check the multipart features parameter when running the Dissolve tool, the new table returns 2049 sightings. If I uncheck multipart features, the new table results in 2126 sightings. The dissolve fields that I am using are the sightings date and the whales' group ID.

Why two different results?

Thanks in advance!
Jill

IamAG · Answer

I know the original post is a little old, but here is what I think happens...

If you uncheck the "Create multipart features" box, then the dissolve will only occur on spatially coincident features.  Features that have the same value in the field on which you are dissolving, but are not coincident, will not be dissolved.  For instance, I have an asset key for a length of main, but there are five work order points along that main.  Those points are not coincident because they occur at different addresses, but they all have the same water main asset key.  When I run the dissolve tool (on the Asset_Key field), those points do not get dissolved because they are at different locations along the main.  There will still be 5 records in the attribute table and 5 points on the map.

On the other hand, if I check the "Create multipart features" box and run the dissolve tool, then those five points get dissolved into one record in the attribute table, but they will still show up as 5 dots on the map.

The reason it is confusing is that if you run the dissolve tool without multipart features, and you have some coincident points and some non-coincident points, only the coincident points will be dissolved.  This results in different than expected record counts.

Using multipart features dissolves all duplicate values, but if you uncheck multipart features, then only some duplicate values may be dissolved (if they are coincident).

Hope that helps.

LucasChaparroVasconsellos · Answer

Create multipart joins elements with the same field your dissolving that are spatially separated. That's the behavior when dissolving shapes

Jill_Clogston · Answer

Thank you Husam.

I'm trying to understand what the difference is between checking the "Create multipart features" parameter vs not checking it when dissolving as when I did it both ways, it returned two different whale sightings counts.