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<h3>Options</h3>
This dialog allows you to select some basic options for QGIS. There are eight tabs:
<p>
<a href="#general">General</a><br/>
<a href="#ren">Rendering & SVG</a><br/>
<a href="#map">Map tools</a><br/>
<a href="#over">Overlay</a><br/>
<a href="#digit">Digitizing</a><br/>
<a href="#crs">CRS</a><br/>
<a href="#loc">Locale</a><br/>
<a href="#net">Network & Proxy</a><br/>
<a name="general">
<h4>General</h4>
</a>
On this tab you can set general options for project behavior on opening/saving, default map appearance, your favorite icon theme and many others.
<a name="ren">
<h4>Rendering & SVG</h4>
</a>
Within this tab you can set general rendering options for map layers.<br>
By default, QGIS renders all visible layers whenever the map canvas must be refreshed. The events that trigger a refresh of the map canvas include:
<ul>
<li>Adding a layer
<li>Panning or zooming
<li>Resizing the QGIS window
<li>Changing the visibility of a layer or layers
</ul>
QGIS allows you to control the rendering process in a number of ways:<p>
You can set an option to always load new layers without drawing them.<br>
This means the layer will be added to the map, but its visibility check box in the legend will be unchecked by default. To set this option, uncheck the <label>By default new layers added to the map should be displayed</label> check box.<p>
You can set an option to update the map display as features are drawn. <br>
By default, QGIS does not display any features for a layer until the entire layer has been rendered. To update the display as features are read from the data store, set the <label>Number of features to draw before updating the display</label> to an appropriate value. Setting a value of 0 disables update during drawing (this is the default). Setting a value too low will result in poor performance as the map canvas is continually updated during the reading of the features. A suggested value to start with is 500.
<a name="map">
<h4>Map tools</h4>
</a>
<h5>Identify</h5>
The <label>Mode</label> setting determines which layers will be shown by the <label>Identify</label> tool. By switching to <label>Top down</label> instead of <label>Current layer</label> attributes for all identifiable layers will be shown with the <label>Identify</label> tool.
<h5>Measure tool</h5>
Here you can set an ellipsoid for distance calculations, measurement units and preferred color of rubber band.
<h5>Panning and zooming</h5>
Allows defining mouse wheel action and zoom factor.
<a name="over">
<h4>Overlay</h4>
</a>
Define placement algorithm for labels. Choose between <label>central point (fastest)</label>, <label>chain (fast)</label>, <label>popmusic tabu chain (slow)</label>, <label>popmusic tabu (slow)</label> and <label>popmusic chain (very slow)</label>.
<a name="digit">
<h4>Digitizing</h4>
</a>
<h5>Rubber band</h5>
In the <label>Digitizing</label> tab you can define settings for digitizing line width and color.
<h5>Snapping</h5>
Here you can define a general, project wide snapping tolerance. <p>
You can select between <label>To vertex</label>, <label>To segment</label> or <label>To vertex and segment</label> as default snap mode. You can also define a default snapping tolerance and a search radius for vertex edits. The tolerance can be set either in map units or in pixels. The advantage of choosing pixels, is that the snapping tolerance doesn't have to be changed after zoom operations.<p>
A layer based snapping tolerance can be defined by choosing <label>Settings</label> (or <label>File</label>) > <label>Project Properties...</label>. In the <label>General</label> tab, section <label>Digitize</label> you can click on <label>Snapping options...</label> to enable and adjust snapping mode and tolerance on a layer basis.
<h5>Vertex markers</h5>
You can define marker style as <label>Semi transparent circle</label>, <label>Cross</label> or <label>None</label> and size; you can also set showing markers only for selected features.
<h5>Enter attribute values</h5>
By default, after digitizing a new feature, QGIS asks you to enter attribute values for that feature. Ticking <label>Suppress attributes pop-up windows after each created feature</label> allows you to enter the attributes later.
<a name="crs">
<h4>CRS</h4>
</a>
QGIS no longer sets the map CRS to the coordinate reference system of the first layer loaded. When you start a QGIS session with layers that do not have a CRS, you need to check and define the CRS definition for these layers. This can be done globally on this tab.<p>
The global default CRS <i>proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs</i> comes predefined in QGIS but can of course be changed, and the new definition will be saved for subsequent QGIS sessions.
<a name="lov">
<h4>Locale</h4>
</a>
Informs you about active system locale. To change it tick <label>Override system locale</label> and restart QGIS.
<a name="net">
<h4>Network & Proxy</h4>
</a>
Tick <label>Use proxy for web access</label> to define host, port, user, and password.
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