Using split tool in ArcGIS Pro shapefile results in different dimensions in ArcMap

[JoelCrawford2]

I work in county government and we are currently in a transitional phase in GIS software - we currently use both ArcMap 10.8.2 and ArcGIS Pro 3.2.0.  We've recently noticed some odd discrepancies in reported distances after splitting polygons in a shapefile in ArcGIS Pro and then viewing that same shapefile in ArcMap.  We are using the same county coordinate system and units (US feet) in both versions of the software.

For example, I'll create a simple square polygon in a shapefile in ArcGIS Pro that is exactly 3000 ft by 3000 ft:

I then open the same shapefile with the same coordinate system in ArcMap 10.8.2 - everything measures out as it should:

However if I take that same polygon in ArcGIS Pro, measure exactly 1500 ft from a corner and split off a portion:

It appears like this in ArcMap 10.8.2:

Instead of the 1500 feet as it was split in Pro, it now shows the measurement from the corner to the split location as 1500.001082 feet.  The split also seems to have modified the north/south dimension as well:

Bringing the shapefile back into ArcGIS Pro - the measurements list out exactly as we split them - a 3000 ft x 3000 ft square split 1500 ft from the bottom corner.

The difference measured is indeed very, very small - but we are at a loss at why there would be any difference - especially when using the same units and coordinate system.  There are also concerns that this could introduce tiny gaps or overlaps in split data that is being using in both ArcMap and ArcPro.

Hopefully someone has some ideas on why we're seeing these differences when using the split tool - thank you in advance!

[Scott_Harris]

@JoelCrawford2 

Have you tried to create a topology with cluster tolerance equal to the XY tolerance of your data? You can add a Must Not Have Gaps and a Must Not Overlap rule to the polygons and test if Split in ArcGIS Pro is introducing gaps that are larger than the XY tolerance. 

[LyonMNGIS]

@Scott_Harris 

I really don't think we should need topology to perform basic splits. 

In the following images I split a polygon by tracing a road.  The first image shows that the polygon boundary and roads are all perfectly snapped,  The second image shows that the new polygon no longer is aligned to the road or the other polygon(s) that were not split.  Is this a bug? 

[Scott_Harris]

@LyonMNGIS I suggested topology as way to find out more information in researching if this was a bug.

In your screenshot, you show the map scale being 1:0.05, approaching the XY resolution and XY tolerance of the data. If I had to guess, the distance between the points is within the XY tolerance, but hard to tell from here. A topology might help answer that question.

[JoelCrawford2]

I have not created a topology for this case, mainly because it's just a basic shapefile, which I didn't think could use topology rules - but I could be wrong on that.  I can give that a shot and see what it gives me - but it still doesn't really explain why I'm seeing different numbers, especially when splitting polygons by whole numbers (1500 ft).  The points made by @MErikReedAugusta are interesting, specifically the process running in meters and then converting back to US Feet - those trailing numbers certainly kind of feel like a slight difference in conversion between ArcMap & Pro.

[MErikReedAugusta]

The first thing I note is that the two programs don't report measurements to the same level of precision.  ArcMap provides 6 decimal points, whereas I can only get 2 decimal points out of ArcPro.

So I have to wonder if there's actually any difference, or if these are just rounding errors.

If they're not display rounding errors, they might be conversion rounding errors.  This almost looks like the sort of discrepancy I'd expect between Foot (US) and Foot (Int'l).  I have a feeling the "back-end" runs on meters, for both programs.  But are they converting to the two foot specs equally?

[Scott_Harris]

@MErikReedAugusta FYI you can get more precision from the measure tool in ArcGIS Pro. You just have to change the numeric formatting of the Distance Units that you are measuring in:

[MErikReedAugusta]

Good to know, Scott!  I knew that setting had to be in there somewhere, but I'd never gone spelunking for it, and didn't have time to do so this morning.  Greatly appreciated!

@JoelCrawford2, go into these settings and set your distance unit to be 6 decimal places, and repeat your experiment.  Are the numbers still different, or are they the same?

[JoelCrawford2]

@MErikReedAugusta  - I was thinking the same thing.  I changed my measurement settings in Pro to match the six digits I see when measuring in ArcMap.  Repeating the experiment, I created another 3000 x 3000 ft square in Pro - note the measure tool shows this as 3000.000000 ft US:

Then, I split the polygon at exactly 1500 ft.  The difference this time, is with the extra digits being displayed I'm now seeing the 1500.001036 ft US as I would see in ArcMap:

Finally, as an added experiment, I created a the same square in ArcMap, and split it at 1500 ft in ArcMap.  It measures out as exactly 1500 feet in both ArcMap and Pro:

This appears to confirm that there is a different process/unit conversion going on when splitting polygons in ArcGIS Pro vs. ArcMap.  I did test out a topology rule to make sure I'm not getting splits/overlaps, which I am not since these numbers are smaller than the standard XY tolerance. 

However, I still think we shouldn't be seeing changes in dimensions in Pro (no matter how small) when performing splits, because we didn't see those changes when performing splits in ArcMap.