General Tools¶

Keyboard shortcuts¶

QGIS provides default keyboard shortcuts for many features. You can find them in section Menu Bar. Additionally, the menu option Settings ‣ Configure Shortcuts... allows you to change the default keyboard shortcuts and add new keyboard shortcuts to QGIS features.

Figure Shortcuts 1:

Define shortcut options

Configuration is very simple. Just select a feature from the list and click on :

• [Change] and press the new combination you want to assign as new shortcut
• [Set none] to clear any assigned shortcut
• or [Set default] to backup the shortcut to its original and default value.

Once you have finished your configuration, you can save it as an XML file and load it to another QGIS installation.

Context help¶

When you need help on a specific topic, you can access context help via the [Help] button available in most dialogs — please note that third-party plugins can point to dedicated web pages.

Rendering¶

By default, QGIS renders all visible layers whenever the map canvas is refreshed. The events that trigger a refresh of the map canvas include:

• Adding a layer
• Panning or zooming
• Resizing the QGIS window
• Changing the visibility of a layer or layers

QGIS allows you to control the rendering process in a number of ways.

Color Selector¶

The select color dialog will appear whenever you push the icon to choose a color. The features of this dialog depends on the state of the Use native color chooser dialogs parameter checkbox in Settings ‣ Options ‣ General menu. When checked, the color dialog used is the one of the OS being used. Otherwise, QGIS custom color chooser is used.

This dialog has four different tabs which allow you to select colors by ^{color ramp}, ^{color wheel}, ^{color swatches} or ^{color picker} (not available under ).

Whatever method you use, the selected color is always described through color sliders for HSV (Hue, Saturation, Value) and RGB (Red, Green, Blue) values. There is also an opacity slider to set transparency level. On the lower left part of the dialog you can see a comparison between the current and the new color you are presently selecting and on the lower right part you have the option to add the color you just tweaked into a color slot button.

Figure color selector 1:

Color selector ramp tab

With ^{color ramp} or with ^{color wheel}, you can browse to all possible color combinations. There are other possibilities though. By using ^{color swatches} you can choose from a preselected list. This selected list is populated with one of three methods:

• Recent colors,
• Standard colors, a user-defined list of colors set under Settings ‣ Options ‣ Colors menu
• or Project colors, a user-defined list of colors set under Project ‣ Project Properties ‣ Default Styles.

Figure color selector 2:

Color selector switcher tab

Another option is to use the ^{color picker} which allows you to sample a color from under your mouse pointer at any part of QGIS or even from another application by pressing the space bar. Please note that the color picker is OS dependent and is currently not supported by OSX.

Figure color selector 3:

Quick color selector menu

Blending Modes¶

QGIS offers different options for special rendering effects with these tools that you may previously only know from graphics programs. Blending modes can be applied on layers, on features but also on print composer items:

• Normal: This is the standard blend mode, which uses the alpha channel of the top pixel to blend with the pixel beneath it. The colors aren’t mixed.
• Lighten: This selects the maximum of each component from the foreground and background pixels. Be aware that the results tend to be jagged and harsh.
• Screen: Light pixels from the source are painted over the destination, while dark pixels are not. This mode is most useful for mixing the texture of one item with another item (e.g., you can use a hillshade to texture another layer).
• Dodge: Dodge will brighten and saturate underlying pixels based on the lightness of the top pixel. So, brighter top pixels cause the saturation and brightness of the underlying pixels to increase. This works best if the top pixels aren’t too bright; otherwise the effect is too extreme.
• Addition: This blend mode simply adds pixel values of one item with the other. In case of values above one (in the case of RGB), white is displayed. This mode is suitable for highlighting features.
• Darken: This creates a resultant pixel that retains the smallest components of the foreground and background pixels. Like lighten, the results tend to be jagged and harsh.
• Multiply: Here, the numbers for each pixel of the top item are multiplied with the corresponding pixels for the bottom item. The results are darker pictures.
• Burn: Darker colors in the top item cause the underlying items to darken. Burn can be used to tweak and colorise underlying layers.
• Overlay: This mode combines the multiply and screen blending modes. In the resulting picture, light parts become lighter and dark parts become darker.
• Soft light: This is very similar to overlay, but instead of using multiply/screen it uses color burn/dodge. This is supposed to emulate shining a soft light onto an image.
• Hard light: Hard light is also very similar to the overlay mode. It’s supposed to emulate projecting a very intense light onto an image.
• Difference: Difference subtracts the top pixel from the bottom pixel, or the other way around, to always get a positive value. Blending with black produces no change, as the difference with all colors is zero.
• Subtract: This blend mode simply subtracts pixel values of one item from the other. In case of negative values, black is displayed.

Zooming and Panning¶

QGIS provides tools to zoom and pan to your area of interest.

Apart from using the ^pan and ^zoom-in / ^zoom-out icons on the toolbar with the mouse, navigating can also be done with the mouse wheel, spacebar and the arrow keys.

Measuring¶

QGIS provides four means of measuring geometries:

• the interactive measurement tools ,
• measuring in the ^{Field Calculator},
• derived measures in the Identify features tool,
• and a vector analysis tool: Vector ‣ Geometry Tools ‣ Export/Add Geometry Columns

Measuring works within projected coordinate systems (e.g., UTM) and unprojected data. The first three measuring tools behave equally to global project settings:

If “on the fly” CRS transformation is enabled, the default measurement metric is - different from most other GIS - ellipsoidal, using the ellipsoid defined in File ‣ Project properties ‣ General. This is true both when geographic and projected coordinate systems are defined for the project. If you want to calculate the projected / planimetric area or distance using cartesian maths, the measurement ellipsoid has to be set to “None / Planimetric” (File ‣ Project properties ‣ CRS). However, with a geographic (= unprojected) CRS defined for the data and project, area and distance measurement will be ellipsoidal. If “on the fly” CRS transformation is disabled, the measurement metric is planimetric when the project coordinate system is projected and ellipsoidal when the project coordinate system is unprojected / geographic.

However, neither the identify tool nor the field calculator will transform your data to the project CRS before measuring. If you want to achieve this, you have to use the vector analysis tool: Vector ‣ Geometry Tools ‣ Export/Add Geometry Columns. Here, measurement is by default planimetric except if you choose the ellipsoidal measure.

Measure length, areas and angles interactive¶

All measuring modules use the snapping settings from the digitizing module. This is useful, if you want to measure along lines or areas in vector layers.

To select a measuring tool, click on and select the tool you want to use.

By default, ^{Measure Line}: QGIS measures real distances between given points according to a defined ellipsoid. You can define a rubberband color and your preferred measurement units (meters or feet) and angle units (degrees, radians and gon) in the menu option Settings ‣ Options ‣ Map Tools. The tool then allows you to click points on the map. Each segment length, as well as the total, shows up in the measure window. To stop measuring, click your right mouse button. Note that you can interactively change the measurement units in the measurement dialog. It overrides the Preferred measurement units in the options. There is an info section in the dialog that shows which CRS settings are being used during measurement calculations.

Figure Measure 1:

Measure Distance

^{Measure Area}: Areas can also be measured. In the measure window, the accumulated area size appears. In addition, the measuring tool will snap to the currently selected layer, provided that layer has its snapping tolerance set (see section Setting the Snapping Tolerance and Search Radius). So, if you want to measure exactly along a line feature, or around a polygon feature, first set its snapping tolerance, then select the layer. Now, when using the measuring tools, each mouse click (within the tolerance setting) will snap to that layer.

Figure Measure 2:

Measure Area

^{Measure Angle}: You can also measure angles. The cursor becomes cross-shaped. Click to draw the first segment of the angle you wish to measure, then move the cursor to draw the desired angle. The measure is displayed in a pop-up dialog.

Figure Measure 3:

Measure Angle

Select and deselect features¶

The QGIS toolbar provides several tools to select features in the map canvas. To select one or several features, just click on and select your tool:

• ^{Select Features by area or single click} to select feature(s) either by simple click or by rectangle
• ^{Select Features by Polygon}
• ^{Select Features by Freehand}
• ^{Select Features by Radius}

To deselect all selected features, click on ^{Deselect Features from All Layers}.

^{Select features using an expression} allows user to select features using expression dialog. See Expressions chapter for some example.

Users can save selected features into a New Memory Vector Layer or a New Vector Layer using Edit ‣ Copy Features and Edit ‣ Paste Features as in the wanted format.

Data defined override setup¶

Beside many options in the vector layer properties dialog or settings in the print composer, you can find a ^{Data defined override} icon. Thanks to expressions based on layer attributes or item settings, prebuild or custom functions and variables, this tool allows you to set dynamic value for the concerned parameter. When enabled, the value returned by this widget is applied to the parameter regardless its normal value (checkbox, textbox, slider...).

Clicking the ^{Data defined override} icon shows:

• a Description ... that indicates if it is enabled, which input expected, valid input type and the current definition,
• an entry to list the Field type available,
• an entry to list the Variable available,
• Edit ... button to create or edit the expression to use,
• Paste and Copy buttons,
• Clear button to remove the setup.

Parameters that can be used with data-defined tools are:

• Style and symbols parameters
• Labels parameters
• Composer parameters

Identify features¶

The Identify tool allows you to interact with the map canvas and get information on features in a pop-up window. To identify features, use View ‣ Identify features or press Ctrl + Shift + I, or click the ^{Identify features} icon on the Attributes toolbar.

QGIS offers two ways to identify features with the ^{Identify features} tool:

• left click will identify features according to the mode set in the Identify results panel
• right click will fetch all the snapped features from all the visible layers. This will open a context menu, allowing the user to choose more precisely the features to identify.

If you click on feature(s), the Identify results dialog will list information about the clicked feature(s). The default view is a tree view where the first item is the name of the layer and its children are its identified feature(s). Each feature is described by the name of a field along with its value. This field is the one set in Properties ‣ Display. Then follows all the other information about the feature.

This window can be customized to display custom fields, but by default it will display three kinds of information:

• Actions: Actions can be added to the identify feature windows. The action is run by clicking on the action label. By default, only one action is added, namely view feature form for editing. You can define more actions in the layer’s properties dialog.
• Derived: This information is calculated or derived from other information. This includes the feature id, its length or perimeter and area in map units depending on its geometry, the count of spatial parts and the number of the clicked part in case of multi-geometry, the count of vertices in the feature and the number of the closest one to the point clicked. It also reports the X and Y (and Z/M if available) coordinate values of both clicked point and feature closest vertex.
• Data attributes: This is the list of attribute fields and values for the feature that has been clicked.

Figure Identify 1:

Identify features dialog

At the top of the window, you have seven icons:

• ^{Expand tree}
• ^{Collapse tree}
• ^{Default behavior} to define whether next identified features information should be collapsed or expanded
• ^{View the feature form}
• ^{Clear Results}
• ^{Copy selected feature to clipboard}
• ^{Print selected HTML response}

At the bottom of the window, you have the Mode and View comboboxes. With the Mode combobox you can define from which layers features should be identified:

• ‘Current layer’ : only features from the selected layer are identified. The layer may not be visible in the canvas.
• ‘Top down, stop at first’: for only features from the upper visible layer.
• ‘Top down’: for all features from the visible layers. The results are shown in the panel.
• and ‘Layer selection’: opens a context menu where the user selects the layer to identify features from. Operates like a right-click. Only the chosen features will be shown in the result panel.

The View can be set as ‘Tree’, ‘Table’ or ‘Graph’. ‘Table’ and ‘Graph’ views can only be set for raster layers.

The identify tool allows you to auto open a form. If checked, each time a single feature is identified QGIS will open a form showing its attributes. This is a handy way to quickly edit a feature’s attributes.

Other functions can be found in the context menu of the identified item. For example, from the context menu you can:

• View the feature form
• Zoom to feature
• Copy feature: Copy all feature geometry and attributes
• Toggle feature selection: Adds identified feature to selection
• Copy attribute value: Copy only the value of the attribute that you click on
• Copy feature attributes: Copy the attributes of the feature
• Clear result: Remove results in the window
• Clear highlights: Remove features highlighted on the map
• Highlight all
• Highlight layer
• Activate layer: Choose a layer to be activated
• Layer properties: Open layer properties window
• Expand all
• Collapse all

Annotation Tools¶

The ^{Text Annotation} tool in the attribute toolbar provides the possibility to place formatted text in a balloon on the QGIS map canvas. Use the Text Annotation tool and click into the map canvas.

Figure annotation 1:

Annotation text dialog

Double clicking on the item opens a dialog with various options. There is the text editor to enter the formatted text and other item settings. For instance, there is the choice of having the item placed on a map position (displayed by a marker symbol) or to have the item on a screen position (not related to the map). The item can be moved by map position (by dragging the map marker) or by moving only the balloon. The icons are part of the GIS theme, and they are used by default in the other themes, too.

The ^{Move Annotation} tool allows you to move the annotation on the map canvas.

Form annotations¶

Additionally, you can also create your own annotation forms. The ^{Form Annotation} tool is useful to display attributes of a vector layer in a customized Qt Designer form (see figure_custom_annotation). This is similar to the designer forms for the Identify features tool, but displayed in an annotation item. Also see this video https://youtu.be/0pDBuSbQ02o?t=2m25s from Tim Sutton for more information.

Figure annotation 2:

Customized qt designer annotation form

註解

If you press Ctrl+T while an Annotation tool is active (move annotation, text annotation, form annotation), the visibility states of the items are inverted.

Spatial Bookmarks¶

Spatial Bookmarks allow you to “bookmark” a geographic location and return to it later. Bookmarks are saved on the computer, meaning that they are available from any project in the same computer.

Nesting Projects¶

If you want to embed content from other project files into your project, you can choose Layer ‣ Embed Layers and Groups.

Embedding layers¶

The following dialog allows you to embed layers from other projects. Here is a small example:

1. Press to look for a project from the Alaska dataset.
2. Select the project file relations.qgs. You can see the content of the project (see figure_embed_dialog).
3. Press Ctrl and click on the layers airports and regions. Press [OK]. The selected layers are embedded in the map legend and the map view now.

Figure Nesting 1:

Select layers and groups to embed

While the embedded layers are editable, you can’t change their properties like style and labeling.

Decorations¶

The Decorations of QGIS include the Grid, the Copyright Label, the North Arrow and the Scale Bar. They are used to ‘decorate’ the map by adding cartographic elements.

Grid¶

^Grid allows you to add a coordinate grid and coordinate annotations to the map canvas.

Figure Decorations 1:

The Grid Dialog

1. Select from menu View ‣ Decorations ‣ Grid. The dialog starts (see figure_decorations_1).
2. Activate the Enable grid checkbox and set grid definitions according to the layers loaded in the map canvas.
3. Activate the Draw annotations checkbox and set annotation definitions according to the layers loaded in the map canvas.
4. Click [Apply] to verify that it looks as expected or [OK] if you’re satisfied.

Copyright Label¶

^{Copyright label} adds a copyright label using the text you prefer to the map.

Figure Decorations 2:

The Copyright Dialog

1. Select from menu View ‣ Decorations ‣ Copyright Label. The dialog starts (see figure_decorations_2).
2. Make sure the Enable Copyright Label checkbox is checked.
3. Enter the text you want to place on the map. You can use HTML as shown in the example.
4. Choose the placement of the label from the Placement combo box.
5. You can refine the placement of the item by setting a Horizontal and/or Vertical Marging from (Canvas) Edge. These values can be a distance in Millimeter or Pixels or set as Percentage of the width or height of the map canvas.
6. You can change the color to apply.
7. Click [Apply] to verify that it looks as expected or [OK] if you’re satisfied.

In the example above, which is the default, QGIS places a copyright symbol followed by the date in the lower right-hand corner of the map canvas.

North Arrow¶

^{North Arrow} places a simple north arrow on the map canvas. Currently, there is only one style available. You can adjust the angle of the arrow or let QGIS set the direction automatically. If you choose to let QGIS determine the direction, it makes its best guess as to how the arrow should be oriented. For placement of the arrow, you have four options, corresponding to the four corners of the map canvas. You can refine the placement of the arrow by setting a Horizontal and/or Vertical Marging from (Canvas) Edge. These values can be a distance in Millimeter or Pixels or set as Percentage of the width or height of the map canvas.

Figure Decorations 3:

The North Arrow Dialog

Scale Bar¶

^{Scale Bar} adds a simple scale bar to the map canvas. You can control the style and placement, as well as the labelling of the bar.

Figure Decorations 4:

The Scale Bar Dialog

QGIS only supports displaying the scale in the same units as your map frame. So if the units of your layers are in meters, you can’t create a scale bar in feet. Likewise, if you are using decimal degrees, you can’t create a scale bar to display distance in meters.

To add a scale bar:

1. Select from menu View ‣ Decorations ‣ Scale Bar. The dialog starts (see figure_decorations_4).
2. Make sure the Enable scale bar checkbox is checked.
3. Choose the style from the Scale bar style combo box.
4. Select the color for the bar Color of bar or use the default black color.
5. Set the Size of bar .
6. Optionally, check Automatically snap to round number on resize to display values easy-to-read.
7. Choose the placement from the Placement combo box.
8. You can refine the placement of the item by setting a Horizontal and/or Vertical Marging from (Canvas) Edge. These values can be a distance in Millimeter or Pixels or set as Percentage of the width or height of the map canvas.
9. Click [Apply] to verify that it looks as expected or [OK] if you’re satisfied.

小技巧

Settings of Decorations

When you save a .qgs project, any changes you have made to Grid, North Arrow, Scale Bar and Copyright will be saved in the project and restored the next time you load the project.

Authentication¶

QGIS has facility to store/retrieve authentication credentials in a secure manner. Users can securely save credentials into authentication configurations, which are stored in a portable database, can be applied to server or database connections, and safely referenced by their ID tokens in project or settings files. For more information see Authentication System.

A master password needs to be set up when initializing the authentication system and its portable database.

Save layer into file¶

Layers (raster or vector) can be saved in another format with the Save As... feature in the layer contextual menu (by right-clicking in the layer in the layer tree) or in the Layer ‣ Save As... menu.

The Save As dialog shows several parameters to change the behaviour when saving the layer. Common parameters (raster and vector) are:

• Format
• Filename
• CRS
• Add save file to map to add the new layer to the canvas
• Extent (possible values are layer, Map view or custom extent)
• Create (for raster), Layer or Custom (for vector) Options which allow you to change some advanced options. Advanced user can see the driver documentation in gdal-ogr documentation.

However, some parameters are specific to raster and vector formats:

• Raster specific parameters:
  • Resolution (horizontal and vertical)
  • Pyramid creation
  • Output mode (raw data or rendered image)
• Vector specific parameters:
  • Encoding
  • Save only selected features
  • Skip attribute creation
  • Symbology export: can be used mainly for DXF export and for all file formats who manage OGR feature styles (see note below) as DXF, KML, tab file formats:
    • No symbology: default style of the application that reads the data
    • Feature symbology: save style with OGR Feature Styles (see note below)
    • Symbol Layer symbology: save with OGR Feature Styles (see note below) but export the same geometry multiple times if there are multiple symbology symbol layers used
  • Geometry:
    • force to multi-geometry,
    • add z-dimension,
    • add or remove a geometry column with the drop-down list. This is not linked with the current geometry type of the layer. You can add an empty geometry column to an attribute table, remove the geometry column of a spatial layer.

Use of variables for dynamic content¶

You can define custom variables for use in expressions. Variables can be defined at the application global level, project level, layer level and composition level. Just like CSS cascading rules, variables can be overwritten - eg, a project level variable will overwrite any application level variables set. You can use these variables to build text strings or other custom expressions using @ character before the variable name. For example in composer creating a label with this content:

This map was made using QGIS [% @qgis_version %]. The project file for this
map is: [% @project_path %]

Will render the label like this:

This map was made using QGIS 2.14. The project file for this map is:
/gis/qgis-user-conference-2015.qgs

You can manage global variables from the Settings ‣ Options menu, and project level variables from Project properties (including adding your own custom variables).

Figure Variables dialog 2:

Edit variable at the project level