Bug report #6096
Negative values are classified incorrectly using new symbology
Status: | Closed | ||
---|---|---|---|
Priority: | Normal | ||
Assignee: | - | ||
Category: | Symbology | ||
Affected QGIS version: | master | Regression?: | No |
Operating System: | Easy fix?: | No | |
Pull Request or Patch supplied: | No | Resolution: | |
Crashes QGIS or corrupts data: | No | Copied to github as #: | 15442 |
Description
In the new symbology mode, at least in 1.8.0, several classification modes render negative real values as though they were positive values. This occurs with Quantile, Natural Breaks and Standard Deviation classifications. It also fails completely to classify percentages stored as reals (-1 to 1) in Equal Interval and Pretty Breaks modes.
I have import data (from either CSV or XLS) and join it to a vector layer. The data is attached, although with identifying information stripped out because it's embargoed.
The values range from -0.0791 to 0.0165 and are stored as reals. The classifications are a mess; for instance, here's the classification in Quantile mode, in order from lightest color to darkest for 7 categories:
0.0000 - -0.0342
-0.0342 - -0.0185
-0.0185 - 0.0000
0.0000 - 0.0000
0.0000 - 0.0000
0.0000 - 0.0000
0.0000 - 0.0165
I don't know why it includes three categories of 0-0, but it leads to misleading categorization. The data has a MIN of -0.0791 so it should be something like
-0.0791 - -0.0345
-0.0342 - -0.0185
-0.0185 - 0.0000
0.0000 - 0.0165
off the top of my head, although of course that's only 4 categories. There are 56 data points, so it's not for lack of trying.
Associated revisions
History
#1 Updated by Giovanni Manghi about 12 years ago
- Status changed from Open to Feedback
- Category set to Symbology
Can you check if this is a regression since 1.7.4?
#2 Updated by Wes Meltzer about 12 years ago
Giovanni Manghi wrote:
Can you check if this is a regression since 1.7.4?
Short answer: no. I never upgraded from 1.7.1 to 1.7.4 (lazy) but this issue is present in 1.7.1. It's hard to believe I never had a data set consisting of mostly negative reals with 1.7!
Note: I discovered one issue that is a red herring. The weirdness with the excess 0.00 values listed above is actually a problem with the dataset the database reporter generated, which only showed up in quantiles mode. Too many null values. This is not an issue with the Quantiles categorization. The negative numbers issue remains if I change the mode, however.
Here is the Jenks categorization for 1.7.1 and 1.8.0:
0.0000 - -0.0714
-0.0714 - -0.0420
-0.0420 - -0.0282
-0.0282 - -0.0185
-0.0185 - -0.0083
-0.0083 - 0.0030
0.0030 - 0.0165
which is still erroneous without manually changing the order of processing. Top line should be -0.0791 - -0.0714.
#3 Updated by Giovanni Manghi about 12 years ago
- Status changed from Feedback to Open
- Target version set to Version 2.0.0
#4 Updated by Nyall Dawson over 11 years ago
By my testing this is fixed by pull request 453:
#5 Updated by Nathan Woodrow over 11 years ago
- Status changed from Open to Closed
Fixed in changeset 7c0746b091498dbe741c34396f7da5bff51030da.