diagramoverlayqgis
Is there a way to locate diagrams and move them wherever you want in QGIS 1.7.4/ 1.8.0?
I created a pie chart under the tab "diagram". I can mark those diagrams with a green box and move them via the label-tool, but they won't change their position in the end. When I create diagrams with the "diagram overlay" tab they cannot even be marked.
Also, what is the difference between "diagram" and "diagram overlay"?
In QGIS 1.8 this type of diagrams is only provided by the "diagram overlay plugin" (See Plugins => Manage Plugins). Once enabled you have in the vector layer properties a new Tab "Overlay" which offers "Bar Chart" in the dropdown.
With QGIS master (soon to be 2.0) it is possible to draw piecharts, histograms and text diagrams with the builtin diagram engine (the diagram overlay plugin has been removed, as it is superseded by this) In the vector layer properties => Diagrams you can choose "histogram" as type.
Unfortunately, with neither of these it is possible to draw "double" bar diagrams.
Try turning off simplification for the layer, under the rendering tab. That might be causing invalid geometries which prevent the diagrams from being placed correctly.
Best Answer
If your diagrams represent values from polygons, here's what I do: Create a new shapefile of centroids ("Vector->Geoprocessing Tools->Polygon Centroids"). This is a point layer with all the data columns from the original polygon. Now edit this point layer, and move the points to wherever you want each chart. And finally recreate the charts from this point layer. THey will appear at each point's location, not necessarily at the actual polygon centroid.
If the charts are from points to begin with, and you still need to move their location, I'd suggest to make a duplicate point layer just for the charts. Edit this duplicate and move the points as necessary. Not very elegant, but it'll work...