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Is there any way to manually classify Graduated Data in Qgis. In ArcGIS I always used to apply first the natural breaks method to find adequate group sizes for good visual interpretation. Afterwards I adjusted slightly the group-size to have nicer breaks.

So if for example breaks from jenks classification would have been:

1-12
13-21
22-42
43-50

than I could change them manually to: 

1-10
11-20
21-40
41-50

by just clicking into the corresponding rows and changing the values.
Anything similar in Qgis?

Besides: Has anybody idea why Qgis always finds different group sizes any time I push on Jenks?

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3
  • 1
    You should post your second question separately, that sounds interesting; maybe a bug. – SaultDon Jan 8 '14 at 17:08
  • I think I understood more less why...the Jenks algorithm is some kind of a partitioning clusteralgorithm that builts groups by maximizing the differences between groups and minimizing the difference inside the groups. Since partitioning algorithms depend on their (randomly chosen) starting arrangement of groups they create different results. – Joschi Jan 9 '14 at 16:16
  • Just to flag - there does seem to be a bug in the Jenks calculations in QGIS 2.x. I've flagged this in other posts before (and to the best of my knowledge it was picked up by Nathan Woodrow) - but even with the latest (stable) version installed it seems to vary. – Andrew Tice Jan 10 '14 at 0:11
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It looks like you can manually adjust the ranges by double clicking the Value under the Value column after creating Graduated classes.

But the label doesn't update so you have to re-enter the new value there too[0].

Changing class ranges in QGIS 2.0.1

[0] - http://hub.qgis.org/issues/9312

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1
  • nice thanks!!! :) legends don't get adjusted unfortunately so there is a lot of manual work when having several classes, but okay. – Joschi Jan 8 '14 at 17:15

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