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How would I go about labeling every other feature in QGIS (1.8)?

For example I have a set of contours every 10 meters from 0m to 100m. How would I label only every 20 meter contour? e.g. label contours 0, 20, 40, 60, 80 and 100m while showing all the contours.

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    In ArcGIS, I have used a mod() query to select the contours I wanted to label, and then labeled only the selected features. This should be possible in QGIS too. Syntax for the query should be something like mod('elev',20)=0 where 'elev' is the contour value. – L_Holcombe Feb 26 '13 at 6:23
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Use the following modulo expression to filter your labels :

"Z" % 20 = 0

You can use rule based labeling :

modulo labelling

Or to give you a useful example, below :

I duplicated my contour layer and filtered the duplicated layer to be able to apply labeling + add a bold style at the same time only on 0/20/40/60/80/100 lines without using any other rules.

filter and modulo

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According to the question

I think following steps will be helpful for you..

1.Select the features you want to label

2.Open attribute table

3.If you don’t have label attributes ready yet: Add two type “real” columns called e.g. “label_x” and “label_y”

4.Invert the selection (3rd button in attribute table window)

5.Open field calculator and fill “label_x” and “label_y” fields of the selected features with 0 values (or any coordinates outside your map extent)

6.Close field calculator and attribute table

7.Save your edits

8.Open the labeling dialog and set “data defined settings” – “x coordinate” and “y coordinate”

9.Enable “Label this layer” and specify the label field

10.Done

For details please visit our admin (@Underdark) blog

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