Combining data with different scales

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12-18-2015 07:04 AM
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New Contributor III

Hello,

I have two feature classes that I want to combine into one feature class but they were created in two different scales. My thought was that I simply loaded both into one feature class and call it done; however, I realize there might be a better way to get this done. Any suggestions?

Thanks,

Ana

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MVP Esteemed Contributor

Just be aware of the boundaries.  I would symbolize one of the layers with just an outline and have a look at the edges.  You don't want to cut out part of the old layer if the new layer has changed borders.  And symmetrical difference isn't what you want, it would be a union which would keep all the good bits and fiddly bits and enable you to decide what to keep and what to discard.  Also check intersect and other tools in the Overlays tools An overview of the Overlay toolset—Help | ArcGIS for Desktop

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MVP Esteemed Contributor

why not leave them separate? Is there a reason that they have to be combined?

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New Contributor III

Both feature classes represent polygons of city boundaries. One feature class is from the Census data and the other is polygon data I gathered directly from the cities themselves. The idea is to delete features from the Census data and replace them with the data I received.

The data is representing the same thing (i.e. cities) so it would be good to have them combined.

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MVP Esteemed Contributor

if the geometries are identical, just to a spatial or attribute join to bring the attributes over.

If the geometries are different, then be aware that you could end up with a whole load of boundary issues.

It would be better to leave the original files alone and combine, if necessary, the good bits of both files,  you then have the originals and it is easier to put something together than to take something apart

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New Contributor III

A spatial join would indeed create a lot of boundary issues. So, I'll just plan on combining the good bits together and, of course, keep the originals separate. Thanks!

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Regular Contributor III

What do you mean when you say different scales does that mean different projections?

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New Contributor III

Both feature classes are in the same projected coordinate system. However, they were created at different scales. One set is from the Census which was created at a standard 1:100,000 scale and the other is a feature class I created using data I received from multiple sources which looks fine. But I am concerned about combining the Census data with the feature class I created. Is there anything I should be aware of or do when I combine them?

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MVP Frequent Contributor

One question that arises is why?  If you are using Census data, why would you want to essentially "move" it to the new city spatial data?  Where do you want to go with this?  I ask this not as a criticism, but as the reason why could very much affect the outcome.  For example, Census data is created with certain assumptions and constraints (including spatial).  I'm not an expert on Census data, but I suspect changing the spatial part may invalidate some of it, so it would be best to know where this is going so as to be able to evaluate whether the outcome will still be valid.

Chris Donohue, GISP

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Regular Contributor III

If you have an Advanced license you may be interested in the Symmetrical Difference—Help | ArcGIS for Desktop sounds like it's BAS time

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New Contributor III

Yes, symmetrical difference would be helpful if I planned on keeping the Census boundaries of the cities I collected. The Census data has over 300 cites but my data only has 40 cities (better quality boundaries). My plan is to remove the 40 cities from the Census data and replace them with my 40. So I'll at least have 40 cities with better boundaries. Does this make sense?

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