Assigning unique IDs to two or more overlapping polygons

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06-28-2012 03:58 AM
RyanWilson1
New Contributor
Hi,
I wonder if anybody could help me with a problem I am having.
I have two shapefile containing glacier polygon outlines of the same area but from different times.
In one shapefile the glaciers polygons are a lot larger, and in the other the same glaciers are smaller with some having split into two or more seperate glacier polygons.

I need to calculate area change for each individual glacier. To do this I am thinking of assigning a unique ID number to each of the overlapping glacier polygons. Once the IDs in both shapefiles correspond to the same glacier I will calulate the area for both in arcmap and then export this data into excel. I can then do a simply subtraction based on the IDs.

I am just struggling with the assigning unique IDs bit. Any help would be much appreciated

Cheers,

Ryan
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markdenil
Regular Contributor II
Try intersecting the two shape files, using ONLY_FID.
This will give you a feature table of the overlaps with fields with the source FIDs for each original shape file.
You might dissolve the output on the two source FID fields, so you have only one record for each early date-late date intersection pair.
Create a new unique id field on this table, with whatever sort of unique id you fancy.
Join this table to each of the original shape files using the appropriate source FID field in the dissolved intersect file
Transfer the unique id to a field in each your original shape files.
Remove the joins.

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4 Replies
markdenil
Regular Contributor II
Try intersecting the two shape files, using ONLY_FID.
This will give you a feature table of the overlaps with fields with the source FIDs for each original shape file.
You might dissolve the output on the two source FID fields, so you have only one record for each early date-late date intersection pair.
Create a new unique id field on this table, with whatever sort of unique id you fancy.
Join this table to each of the original shape files using the appropriate source FID field in the dissolved intersect file
Transfer the unique id to a field in each your original shape files.
Remove the joins.
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MarcinGasior
Regular Contributor
You can try Spatial Join (Analysis) tool.
When you spatially join big glaciers to smaller, their attributes will be transfered to smaller ones (look at screenshot below).
(If you have only OBJECTID field, you may need to calculate new ID field based on OBJECTID).
[ATTACH=CONFIG]15563[/ATTACH]
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RyanWilson1
New Contributor
Thanks for the quick reply guys 🙂 I shall give both of these a go and see how I get on.

Thanks Again,

Ryan
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RyanWilson1
New Contributor
Hi Guys,

Sorry for the slow reply. Managed it with a combination of clipping and intersecting in the end but you two put me on the right track.

Thanks again its much appreciated,

Ryan
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