Bug report #6625
Classes in Natural Braeks (Jenks) Symbology
|Affected QGIS version:||1.8.0||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||15809|
Symbology of a vector layer (shapefile in the test case)--> Graduated Renderer --> Natural Breaks (Jenks) mode.
It seems that Quantum GIS (version 1.8 on WIN XP, using new simbology) propose different intervals (using the same column and number of classes) each time you classify features.
#3 Updated by Diego Mo over 8 years ago
As test case you can use toponomastica_10000_geo.shp (field ROTAZIONE) that you can download from
The pubblication page is http://www.comune.torino.it/geoportale/ser_professionali_2.htm
The problem seems to happen both in Qgis 1.8 and Master(release 2a4d79d)
#4 Updated by Nyall Dawson over 8 years ago
Actually after looking into it this is the intended behaviour -- in order to speed up the calculation the natural breaks classifier takes a random sample from a layer which has a large number of rows (> 1000 rows). When a layer has more than 1000 rows, a random sample of either 1000 values or 10% of the dataset (whichever is larger) is used to calculate the breaks.