The Vector Properties Dialog:Diagram Tab

Diagram Tab

The Diagram tab allows you to add a grahic overlay to a vector layer. To activate this feature, open the Plugin Manager and select the Diagram Overlay' plugin. After this, there is a new tab in the vector Layer Properties dialog where the settings for diagrams may be entered (see figure <A HREF="#fig:diagramtab">13</A>). <P>

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Figure: Vector properties dialog with diagram tab

[clip=true, width=13cm]diagram_tab

<P> The current implementation of diagrams provides support for pie- and barcharts and for linear scaling of the diagram size according to a classification attribute. We will demonstrate an example and overlay the alaska boundary layer a barchart diagramm showing some temperature data from a climate vector layer. Both vector layers are part of the QGIS sample dataset (see Section <A HREF="#label_sampledata"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"

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1. First click on the mActionAddOgrLayerLoad Vector icon, browse to the QGIS sample dataset folder and load the two vector shape layers alaska.shp and climate.shp.
2. Double click the climate layer in the map legend to open the Layer Properties dialog.
3. Click on the Diagram Overlay and select Bar chart as Diagram type.
4. In the diagram we want to display the values of the three columns T_F_JAN, T_F_JAN and T_F_MEAN. First select T_F_JAN as Attributes and click Add attribute, then T_F_JUL and finally T_F_MEAN.
5. For linear scaling of the diagram size we define T_F_JUL as classification attribute.
6. Now click on find maximum value, choose a size value and unit and click Apply to display the diagram in the QGIS main window.
7. You can now adapt the chart size, or change the attribute colors double clicking on the color values in the attribute field. Figure <A HREF="#fig:climatediagram">14</A> gives an impression.
8. Finally click Ok.

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Figure: Diagram from temperature data overlayed on a map

[clip=true, width=13cm]climate_diagram