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QGIS User Guide - OSGeo Download Server

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5.4 Proprietà dei layer vettoriali<br />

• Value map: a combo box with predefined items. The value is stored in the attribute, the description<br />

is shown in the comboo box. You can define values manually or load them from a layer or<br />

a csv file.<br />

• Enumeration: Opens a combo box with values that can be used within the columns type. This<br />

is currently only supported by the postgres provider.<br />

• Immutable: The immutable attribute column is read-only. The user is not able to modify the<br />

content.<br />

5.4.8. General Tab<br />

The General tab is essentially like that of the raster dialog. It allows you to change the display<br />

name, set scale dependent rendering options, create a spatial index of the vector file (only for OGR<br />

supported formats and PostGIS) and view or change the projection of the specific vetor layer.<br />

The Query Builder button allows you to create a subset of the features in the layer - but this button<br />

currently only is available when you open the attribute table and select the ... button next to<br />

Advanced search.<br />

5.4.9. Metadata Tab<br />

The Metadata tab contains general information about the layer, including specifics about the type<br />

and location, number of features, feature type, and the editing capabilities. The Extents section,<br />

providing layer extent information, and the Layer Spatial Reference System section, providing information<br />

about the CRS of the layer. This is a quick way to get information about the layer, but is not<br />

yet editable.<br />

5.4.10. Scheda Azioni<br />

<strong>QGIS</strong> offre la possibilità di effettuare azioni sulla base degli attributi associati ai singoli elementi del<br />

layer vettoriale. Questo permette di effettuare un elevato numero di azioni, per esempio, lanciare un<br />

programma con argomenti costruiti tramite gli attributi delle geometrie o passando i parametri ad uno<br />

strumento di web reporting.<br />

Definire delle azioni è utile quando si voglia lanciare un’applicazione esterna o la visualizzazione di<br />

una pagina web sulla base di uno o più valori associati al layer vettoriale. Ad esempio si può lanciare<br />

una ricerca web basata sul valore di un attributo. Questo concetto è spiegato nel seguente paragrafo.<br />

<strong>QGIS</strong> 1.4.0 <strong>User</strong> <strong>Guide</strong> 59

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