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Comparing Monthly Parcel Update to find changes

amarcz_cc

Hello,

I am attempting to find a quicker way to identify Parcels that update on a monthly basis. For some backstory, I work at a local government who doesn't manage our Parcels in-house and get a monthly update from the County.

I would like assistance in identifying a workflow that will use the APN (not ObjectID) to compare the feature with the newly downloaded datasets. This will be used to show changes in a particular feature whether that be any of the following, new APNs, missing APNs, or geometry changes in identical APNs

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AustinAverill

Take a look at some example code I wrote to check over features. The output is a fgdb table that contains the change and whatever unique identifier, which you could then run a join on or just use the information from the table. Not sure if this would be helpful or not.

https://github.com/AustinNWUD/gis-python-resources/tree/main/featureComparison

amarcz_cc

We update on a monthly basis, the reason for identifying changes between existing and current dataset has to do with our Permitting System and how it deals with changes in APN.

amarcz_cc

Thanks for the idea Vince, however, most of what you said went over my head so I do think that is a viable option for me.

VinceAngelo

I've had good experiences with leveraging an SHA-1 hash of the non-key important data*, storing the hashes with the actual primary key in a parallel table. Due to the nature of the data, I've sometimes converted the data to only a few significant digits, then hashed that (to enable "fuzzy matching", when 3.71 -> 3.72 or 3.68 is not significant, but 8.23 is). Recently I've stored the geometry and non-geometry hashes separately, and have even been able to match rows without a useful rowid key by inverting the hash dictionary spanning tens of millions of features, so that hashes could resolve feature matching at 85-97% accuracy.

Unfortunately, I can't release my code without approval. And in order to make this work , you need to
be really comfortable with endian integer and floating-pint storage representations. I can say the core
code is a set of encoder functions (one for each supported type), which is stored as a bytearray sequence, that is fed into a core Python hashing function. Use of SHA-1 can generate safety warnings, but using it
for hashing (not cryptographic) purposes is perfectly safe.

- V
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*Unimportant data would include a URL that incorporates the primary key and another column, which could be recomputed (or changed at will)

AustinAverill

Are you looking to update a local layer of parcels with the changes or really quickly produce a table of APN's that have changed between the previous dataset and the new dataset that your stakeholders can reference?

amarcz_cc

@George_Thompson Yes, I have and initially was excited for this as on option. However, I am having troubles with this, as it returns the comparison based on the ObjectID. Because the ObjectID is not maintained throughout the process of integrating the dataset with my own, I have not been able to utilize this.

Looking back at how the data is received, it also does not maintain ObjectIDs throughout the same parcel from consecutive updates.

George_Thompson

Have you taken a look at this tool in Pro? https://pro.arcgis.com/en/pro-app/latest/tool-reference/data-management/feature-compare.htm

It may help you obtain the information that you are looking for.

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