I'm worried I'm missing something terribly obvious here: how do you set the alignment (left / centre / right) for feature labels? I'm referring to QGIS 1.8, and using the 'Label' toolbar, rather than Layer Properties labeling.
[GIS] How to align labels using Label toolbar
alignmentlabelingqgis
Related Solutions
In QGIS 2.0, you can create background rectangles, ovals or custom SVG shapes without the need for a plugin. Just go to Layer Properties | Label | Background section.
If you want to code something. This might be a starting point: http://doc.qgis.org/api/qgspallabeling_8cpp_source.html#l04333
Use the following modulo expression to filter your labels :
"Z" % 20 = 0
You can use rule based labeling :
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.
Best Answer
Go to the tab 'Data Defined Settings'. Scroll down to the bottom and the section marked 'Position'. Here you can define where the label will appear but you need attribute fields for this. Add a field to your attributes called (say) 'h_align'. Now set all its values to 'Right'. Now use this field as your Horizontal Alignment option (you must set X and Y coordinates first and you'll need attribute fields for those too).