Options

This dialog allows you to select some basic options for QGIS. There are eight tabs:

General
Rendering & SVG
Map tools
Overlay
Digitizing
CRS
Locale
Network & Proxy

General

On this tab you can set general options for project behavior on opening/saving, default map appearance, your favorite icon theme and many others.

Rendering & SVG

Within this tab you can set general rendering options for map layers.
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: QGIS allows you to control the rendering process in a number of ways:

You can set an option to always load new layers without drawing them.
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 check box.

You can set an option to update the map display as features are drawn.
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 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.

Map tools

Identify
The setting determines which layers will be shown by the tool. By switching to instead of attributes for all identifiable layers will be shown with the tool.
Measure tool
Here you can set an ellipsoid for distance calculations, measurement units and preferred color of rubber band.
Panning and zooming
Allows to define mouse wheel action and zoom factor.

Overlay

Define placement algorithm for labels. Choose between , , , and .

Digitizing

Rubber band
In the tab you can define settings for digitizing line width and color.
Snapping
Here you can define a general, project wide snapping tolerance.

You can select between , or 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.

A layer based snapping tolerance can be defined by choosing (or ) > . In the tab, section you can click on to enable and adjust snapping mode and tolerance on a layer basis.

Vertex markers
You can define marker style as , or and size; you can also set showing markers only for selected features.
Enter attribute values
By default, after digitizing a new feature, QGIS asks you to enter attribute values for that feature. Ticking allows you to enter the attributes later.

CRS

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.

The global default CRS proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs comes predefined in QGIS but can of course be changed, and the new definition will be saved for subsequent QGIS sessions.

Locale

Informs you about active system locale. To change it tick and restart QGIS.

Network & Proxy

Tick to define host, port, user, and password.