Bug report #22038
Inconsistent intervals for similar labels in graduated classification
|Affected QGIS version:||3.4.6||Regression?:||No|
|Operating System:||Easy fix?:||No|
|Pull Request or Patch supplied:||No||Resolution:|
|Crashes QGIS or corrupts data:||No||Copied to github as #:||29852|
There is currently an inconsistent meaning behind a similar appearance when we make a graduated classification.
In the legend label ... meaning we see for QGIS ------ ----------- a - b a ≤ x ≤ b b - c b < x ≤ c c - d c < x ≤ d
Note that the first class has left inclusion but not the others.
We could wrongly expect from reading only the label :
a - b equals to a ≤ x < b b - c equals to b ≤ x < c c - d equals to c ≤ x < d
... or any other scheme actually.
So the same "class interval label" have different interpretations if they are the first or not.
We need a label notation where the endpoints inclusions are explicit, for example :
common French style style ------- ------- [a, b] [a, b] (b, c] ]b, c] (c, d] ]c, d]
... or at least if we keep the basic "a - b" notation then we must use the same interval scheme for all classes.
Note also that some softwares (R for example) use left-open/right-closed intervals by default :
label -------------- meaning ------ ------ --------- (a, b] ]a, b] a < x ≤ b (b, c] ]b, c] b < x ≤ c (c, d] ]c, d] c < x ≤ d
... and some others (like openJUMP) are left-closed/right-open :
label -------------- meaning ------ ------ --------- [a, b) [a, b[ a ≤ x < b [b, c) [b, c[ b ≤ x < c [c, d) [c, d[ c ≤ x < dSo we need :
- to use a consistent scheme for all classes
- to add an option to be able to choose the left-open or right-open scheme
- to add an option to generate the label with the common notation, the French (Bourbaki) notation or any other notation.