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Updating the lower bound of the first bin

July 09 2009 | 0 comments
Categories: Symbology

We have some maps that we periodically update with new data. We map the data using Quantities|Graduated Colors with a Manual classification. When the layer was created, it used the lowest value in the data set as the lower bound of the first bin. Sometimes, however, the new data will have values lower than that so these new values will not be mapped as it doesn't fit into any of the bins. The only way we know to reset the lower bound of the first bin is to change the classification to something else and then back to Manual but this will also reset our breaks and labels. Is there any way to update the lower bound without this hassle?

Mapping Center Answer:

There is not a way to do what you're asking. 

Though one trick I use is to create a dataset that has an artificially low value (and high value), that will force the classification to always work for all the cases you may need in the future--then you could save that as a layer and import the symbology each time you update the layer for your real data.

For anyone else reading, the reason this works is because of the use of a manual classification; in all other cases, the classification algorithms depend on the range of the data, so just changing the lower value would effectively invalidate the classfication.

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