The Layer Properties dialog for a vector layer provides information about the layer, symbology settings and labeling options. If your vector layer has been loaded from a PostgreSQL/PostGIS datastore, you can also alter the underlying SQL for the layer by invoking the Query Builder dialog on the General tab. To access the Layer Properties dialog, double-click on a layer in the legend or right-click on the layer and select Properties from the popup menu.
Figure Vector Properties 1:
The Style menu provides you with a comprehensive tool for rendering and symbolizing your vector data. You can use Layer rendering ‣ tools that are common to all vector data and special symbolizing tools that were designed for the different kinds of vector data.
Since QGIS 2.0 the old symbology is no longer available. In this version the new symbology has been redesigned and revised.
The renderer is responsible for drawing a feature together with the correct symbol. There are four types of renderers: single symbol, categorized, graduated and rule-based. There is no continuous color renderer, because it is in fact only a special case of the graduated renderer. The categorized and graduated renderer can be created by specifying a symbol and a color ramp - they will set the colors for symbols appropriately. For point layers there is a point displacement renderer available. For each data type (points, lines and polygons) vector symbol layer types are available. Depending on the chosen renderer, the Style menu provides different following sections. On the bottom right of the symbology dialog there is a [Symbol] button which gives access to the Style Manager (see Section vector_style_manager). The Style Manager allows you to edit and remove existing symbols and add new ones.
Select and change multiple symbols
The Symbology allows to select multiple symbols and right click to change color, transparency, size, or width of selected entries.
Single Symbol Renderer
The Single Symbol Renderer is used to render all features of the layer using a single user-defined symbol. The properties, that can be adjusted in the Style menu, depend partially on the type of the layer, but all types share the following structure. In the top left part of the menu, there is a preview of the current symbol to be rendered. On the right part of the menu, there is a list of symbols already defined for the current style, prepared to be used via selecting them from the list. The current symbol can be modified using the menu on the right side.
If you click on the first level in the Symbol layers dialog on the left side it’s possible to define basic parameters like Size, Transparency, Color and Rotation. Here the layers are joined together.
Figure Symbology 1:
More detailed settings can be made when clicking on the second level in the Symbol layers dialog. You can define Symbol layers that are combined afterwards. A symbol can consist of several Symbol layers. The following settings are possible:
Note that once you have set the size in the lower levels the size of the whole symbol can be changed with the Size menu in the first level again. The size of the lower levels changes accordingly while the size ratio is maintained. After having done any needed changes, the symbol can be added to the list of current style symbols (using the [Symbol] Save in symbol library) and then easily be used in the future. Furthermore you can use the [Save Style] button to save the symbol as a QGIS layer style file (.qml) or SLD file(.sld). Currently in version 2.0 SLDs can be exported from any type of renderer: single symbol, categorized, graduated or rule-based, but when importing an SLD, either a single symbol or rule-based renderer is created. That means that categorized or graduated styles are converted to rule-based. If you want to preserve those renderers, you have to stick to the QML format. On the other hand, it could be very handy sometimes to have this easy way of converting styles to rule-based.
With the Style manager from the [Symbol] menu you can administrate your symbols. You can add item, edit item, remove item and share item. ‘Marker’ symbols, ‘Line’ symbols, ‘Fill’ patterns and ‘Color ramps’ can be used to create the symbols (see defining_symbols). The symbols are assigned to ‘All Symbols’, ‘Groups’ or ‘Smart groups’ then.
The Categorized Renderer is used to render all features from a layer, using a single user-defined symbol, which color reflects the value of a selected feature’s attribute. The Style menu allows you to select:
The [Advanced] button in the lower right corner of the dialog allows to set the fields containing rotation and size scale information. For convenience, the list in the center of the menu lists the values of all currently selected attributes together, including the symbols that will be rendered.
The example in figure_symbology_2 shows the category rendering dialog used for the rivers layer of the QGIS sample dataset.
Figure Symbology 2:
You can create a custom color ramp choosing New color ramp... from the Color ramp dropdown menu. A dialog will prompt for the ramp type: Gradient, Random, ColorBrewer, and cpt-city. The first three have options for number of steps and/or multiple stops in the color ramp. See figure_symbology_3 for an example of custom color ramp and figure_symbology_3a for the cpt-city dialog.
Figure Symbology 3:
The cpt-city option opens a new dialog with hundreds of themes included ‘out of the box’.
Figure Symbology 3a:
The Graduated Renderer is used to render all the features from a layer, using a single user-defined symbol, whose color reflects the classification of a selected feature’s attribute to a class.
Figure Symbology 4:
Like Categorized Renderer, it allows to define rotation and size scale from specified columns.
Analogue to the categorized rendered, the Style tab allows you to select:
Additionally, you can specify the number of classes and also the mode how to classify features inside the classes (using the Mode list). The available modes are:
The listbox in the center part of the Style menu lists the classes together with their ranges, labels and symbols that will be rendered.
The example in figure_symbology_4 shows the graduated rendering dialog for the rivers layer of the QGIS sample dataset.
The rule-based renderer is used to render all the features from a layer, using rule based symbols, whose color reflects the classification of a selected feature’s attribute to a class. The rules are based on SQL statements. The dialog allows rule grouping by filter or scale and you can decide if you want to enable symbol levels or use only first matched rule.
The example in figure_symbology_5 shows the rule-based rendering dialog for the rivers layer of the QGIS sample dataset.
To create a rule, activate an existing row by clicking on it or click on ‘+’ and click on the new rule. Then press the [Edit rule] button. In the Rule properties dialog you can define a label for the rule. Press the button to open the Expression builder. In the Function List, click on Fields and Values to view all attributes of the attribute table to be searched. To add an attribute to the Field calculator Expression field, double click its name in the Fields and Values list. Generally you can use the various fields, values and functions to construct the calculation expression or you can just type it into the box (see Field Calculator).
Figure Symbology 5:
The point displacement renderer offers to visualize all features of a point layer, even if they have the same location. To do this, the symbols of the points are placed on a displacement circle around a center symbol.
Figure Symbology 6:
Export vector symbology
You have the possibility to export vector symbology from QGIS into the Google .kml, *.dxf and MapInfo.tab files. Just open the right mouse menu of the layer and click on Save selection as ‣ to define the name of the output file and its format. Use the Symbology export menu to save the symbology either as Feature symbology ‣ or as Symbol layer symbology ‣. If you have used symbol layers it is recommended to use the second setting.
The Labels core application provides smart labeling for vector point, line and polygon layers and only requires a few parameters. This new application also supports on-the-fly transformated layers. The core functions of the application have been redesigned. In QGIS 2.0. there are now a number of other features which improve the labeling. The following menus have been created for labeling the vector layers:
Let us see how the new menus can be used for various vector layers.
Labeling point layers
The following steps describe a simple labeling without using the Data defined override functions that are situated next to the drop-down menus.
You can define the text style in the Text menu (see Figure_labels_1 ). A new function is the Type case option where you can influence the text rendering. You have the possibility to render the text ‘All uppercase’, ‘All lowercase’ or ‘Capitalize first letter’. Also, a new function in QGIS 2.0 is the use of blend modes (see blend_modes).
In the Formatting menu you can define a character for a line break in the labels with the wrap label on character function. Use the Formatted numbers option to format the numbers in an attribute table. Here decimal places are inserted. If you enable this option three decimal places ist set by default.
To create a buffer just activate Draw text buffer checkbox in the Buffer menu. The buffer color is variable. Also, a new function in QGIS 2.0 is the use of blend modes (see blend_modes).
If the Color buffer’s fill checkbox is activated, it will interact with partially transparent text and give mixed color transparency results. Turning off the buffer fill fixes that issue (except where the interior aspect of the buffer’s stroke intersects with the text’s fill) and also allows the user to make outlined text.
In the Background menu you can define with Size X and Size Y the shape of your background. Use Size type to insert an additional ‘Buffer’ into your background. The buffer size one is set by default here. The background then consists of the buffer plus the background in Size X and Size Y. You can set a Rotation where you can choose between ‘Sync with label’, ‘Offset of label’ and ‘Fixed’. Using ‘Offset of label’ and ‘Fixed’ you can rotate the background. Define an Offset X,Y with X and Y values and the background will be shifted. When applying Radius X,Y the background gets rounded corners. Again, it is possible to mix the background with the underlying layers in the map canvas using the Blend mode (see blend_modes).
Use the Shadow menu for a user-defined Drop shadow. The drawing of the background is very variable. Choose between ‘Lowest label component’, ‘Text’, ‘Buffer’ and ‘Background’. The Offset angle depends on the orientation of the label. If you choose the Use global shadow checkbox then the zero point of the angle is always oriented to the north and doesn’t depend on the orientation of the label. Influence the appearance of the shadow with the Blur radius. The higher the number, the softer the shadows.
The appearance of the drop shadow can also be altered by choosing a blend mode (see blend_modes).
Choose the Placement menu for the label placement and the labeling priority. Using the Offset from point setting you now have the possibility to use Quadrants to place your label. Additionally you can alter the angle of the label placement with the Rotation setting. Thus, a placement in a certain quadrant with a certain rotation is possible.
In the Rendering menu you can define label and feature options. In the Label options you find the scale-based visibility setting now. You can prevent QGIS from rendering only selected labels with the Show all labels for this layer (including colliding labels) checkbox. In the Feature options you can define if every part of a multipart feature is to be labeled. In QGIS 2.0 now it’s possible to define if the number of features to be labeled is limited and to Discourage labels from covering features.
Figure Labels 1:
Labeling line layers
After that you can define the text style in the Text menu. Here the same settings as for point layers are possible.
Also in the Formatting menu the same settings as for point layers are possible.
The Buffer menu has the same functions as described in section labeling_point_layers .
The Background menu has the same entries as described in section labeling_point_layers .
Also the Shadow menu has the same entries as described in section labeling_point_layers .
In the Placement menu you find special settings for line layers. The label can be placed Parallel, Curved or Horizontal. With the Parallel and Curved option come the following settings: You can define the position Above line, On line and Below line. It’s possible to select several options at once. QGIS will look for the optimal position of the label then. Remember that here you can also use the line orientation for the position of the label. Additionally you can define a Maximum angle between curved characters when selecting the Curved option (see Figure_labels_2 ).
The Rendering menu has nearly the same entries as for point layers. In the Feature options you can now Suppress labeling of features smaller than.
Figure Labels 2:
Labeling polygon layers
In Text menu define the text style. The entries are the same as for point and line layers.
The Formatting menu allows you to format multiple lines like for point and line layers.
As with point and line layers you can create a text buffer in the Buffer menu.
Use the Background menu to create a complex user-defined background for the polygon layer. You can use the menu as well as for the point and line layers.
The entries in the Shadow menu are the same as for point and line layers.
In the Placement menu you find special settings for polygon layers (see Figure_labels_3 ). Offset from centroid, Horizontal (slow), Around centroid, Free and Using perimeter are possible.
In the Offset from centroid settings you can define if the centroid is visible polygon or whole polygon. That means that either the centroid is used for the polygon you can see on the map or the centroid is used for the whole polygon, no matter if you can see the whole feature on the map. You can place your label with the quadrants here and define offset and rotation. The Around centroid setting makes it possible to place the label around the centroid with a certain distance. Again, you can define visible polygon or whole polygon for the centroid. With the Using perimeter settings you can define a position and a distance for the label. For the position Above line, On line, Below line and Line orientation dependend position are possible.
The entries in the Rendering menu are the same as for line layers. You can also use Suppress labeling of features smaller than in the Feature options.
Figure Labels 3:
Using data-defined override for labeling
With the data-defined override functions the settings for the labeling are overwritten by entries in the attribute table. You can activate/deactivate the function with the right-mouse button. Hover over the symbol and you see the information about the data-defined override, including the current definition field. We now describe an example how to use the data-defined override function for the Move label function (see figure_labels_4 ).
Figure Labels 4:
Figure Labels 5:
Figure Fields 1:
Within the Fields menu you also find an edit widget column. This column can be used to define values or a range of values that are allowed to be added to the specific attribute table column. If you click on the [edit widget] button, a dialog opens, where you can define different widgets. These widgets are:
With the Attribute editor layout you can now define builtin forms for data entry jobs (see figure_fields_2). Choose ‘Drag and drop designer’ and an attribute column. Use the Icon to create a category that then will be shown during the digitizing session (see figure_fields_3). Next step will be to assign the relevant fields to the category with the Icon. You can create more categories and use the same fields again. When creating a new category QGIS will insert a new tab for the category in the built in form.
Other options in the dialog are ‘Autogenerate’ and ‘Provide ui-file’. ‘Autogenerate’ just creates Editors for all fields and tabulates them. The ‘Provide ui-file’ option allows you to use complex dialogs made with the Qt-Designer. Using an UI-file allows a large freedom in creating a dialog. For detailed information see http://nathanw.net/2011/09/05/qgis-tips-custom-feature-forms-with-python-logic/ .
QGIS dialogs can have a python function that is called when the dialog is opened. Use this function to add extra logic to your dialogs. An example is (in module MyForms.py):
def open(dialog,layer,feature): geom = feature.geometry() control = dialog.findChild(QWidged,"My line edit")
Reference in Python Init Function like so: MyForms.open
MyForms.py must live on PYTHONPATH, .qgis2/python, or inside the project folder
Figure Fields 2:
Figure Fields 3:
Coordinate Reference System
Figure General 1:
In QGIS 2.0 there is now an own menu for the map tips. It includes a new feature: Map Tip display text in HTML. While you can still choose a Field to be displayed when hovering over a feature on the map it is now possible to insert HTML code that creates a complex display when hovering over a feature. To activate Map Tips, select the menu option View ‣ MapTips.Figure Display 1 shows an example of HTML code.
Figure Display 1:
Figure Display 2:
QGIS provides the ability to perform an action based on the attributes of a feature. This can be used to perform any number of actions, for example, running a program with arguments built from the attributes of a feature or passing parameters to a web reporting tool.
Figure Actions 1:
Actions are useful when you frequently want to run an external application or view a web page based on one or more values in your vector layer. They are devided into 6 types and can be used like this:
There are several examples included in the dialog. You can load them clicking on [Add default actions]. An example is performing a search based on an attribute value. This concept is used in the following discussion.
Attribute actions are defined from the vector Layer Properties dialog. To define an action, open the vector Layer Properties dialog and click on the Actions menu. Go to the Action properties. Select ‘Generic’ as type and provide a descriptive name for the action. The action itself must contain the name of the application that will be executed when the action is invoked. You can add one or more attribute field values as arguments to the application. When the action is invoked any set of characters that start with a % followed by the name of a field will be replaced by the value of that field. The special characters %% will be replaced by the value of the field that was selected from the identify results or attribute table (see using_actions below). Double quote marks can be used to group text into a single argument to the program, script or command. Double quotes will be ignored if preceded by a backslash.
If you have field names that are substrings of other field names (e.g., col1 and col10) you should indicate so, by surrounding the field name (and the % character) with square brackets (e.g., [%col10]). This will prevent the %col10 field name being mistaken for the %col1 field name with a 0 on the end. The brackets will be removed by QGIS when it substitutes in the value of the field. If you want the substituted field to be surrounded by square brackets, use a second set like this: [[%col10]].
Using the Identify Features tool you can open Identify Results dialog. It includes a (Derived) item that contains information relevant to the layer type. The values in this item can be accessed in a similar way to the other fields by using preceeding the derived field name by (Derived).. For example, a point layer has an X and Y field and the value of these can be used in the action with %(Derived).X and %(Derived).Y. The derived attributes are only available from the Identify Results dialog box, not the Attribute Table dialog box.
Two example actions are shown below:
In the first example, the web browser konqueror is invoked and passed a URL to open. The URL performs a Google search on the value of the nam field from our vector layer. Note that the application or script called by the action must be in the path or you must provide the full path. To be sure, we could rewrite the first example as: /opt/kde3/bin/konqueror http://www.google.com/search?q=%nam. This will ensure that the konqueror application will be executed when the action is invoked.
The second example uses the %% notation which does not rely on a particular field for its value. When the action is invoked, the %% will be replaced by the value of the selected field in the identify results or attribute table.
Actions can be invoked from either the Identify Results dialog, an Attribute Table dialog or from Run Feature Action (recall that these dialogs can be opened by clicking Identify Features or Open Attribute Table or Run Feature Action). To invoke an action, right click on the record and choose the action from the popup menu. Actions are listed in the popup menu by the name you assigned when defining the actions. Click on the action you wish to invoke.
If you are invoking an action that uses the %% notation, right-click on the field value in the Identify Results dialog or the Attribute Table dialog that you wish to pass to the application or script.
Here is another example that pulls data out of a vector layer and inserts them into a file using bash and the echo command (so it will only work or perhaps ). The layer in question has fields for a species name taxon_name, latitude lat and longitude long. I would like to be able to make a spatial selection of a localities and export these field values to a text file for the selected record (shown in yellow in the QGIS map area). Here is the action to achieve this:
bash -c "echo \"%taxon_name %lat %long\" >> /tmp/species_localities.txt"
After selecting a few localities and running the action on each one, opening the output file will show something like this:
Acacia mearnsii -34.0800000000 150.0800000000 Acacia mearnsii -34.9000000000 150.1200000000 Acacia mearnsii -35.2200000000 149.9300000000 Acacia mearnsii -32.2700000000 150.4100000000
As an exercise we create an action that does a Google search on the lakes layer. First we need to determine the URL needed to perform a search on a keyword. This is easily done by just going to Google and doing a simple search, then grabbing the URL from the address bar in your browser. From this little effort we see that the format is: http://google.com/search?q=qgis, where QGIS is the search term. Armed with this information, we can proceed:
Make sure the lakes layer is loaded.
Open the Layer Properties dialog by double-clicking on the layer in the legend or right-click and choose Properties from the popup menu.
Click on the Actions menu.
Enter a name for the action, for example Google Search.
For the action, we need to provide the name of the external program to run. In this case, we can use Firefox. If the program is not in your path, you need to provide the full path.
Following the name of the external application, add the URL used for doing a Google search, up to but not included the search term: http://google.com/search?q=
The text in the Action field should now look like this: firefox http://google.com/search?q=
Click on the drop-down box containing the field names for the lakes layer. It’s located just to the left of the [Insert Field] button.
From the drop-down box select ‘NAMES’ and click [Insert Field].
Your action text now looks like this:
To finalize the action click the [Add to action list] button.
This completes the action and it is ready to use. The final text of the action should look like this:
We can now use the action. Close the Layer Properties dialog and zoom in to an area of interest. Make sure the lakes layer is active and identify a lake. In the result box you’ll now see that our action is visible:
Figure Actions 2:
When we click on the action, it brings up Firefox and navigates to the URL http://www.google.com/search?q=Tustumena. It is also possible to add further attribute fields to the action. Therefore you can add a + to the end of the action text, select another field and click on [Insert Field]. In this example there is just no other field available that would make sense to search for.
You can define multiple actions for a layer and each will show up in the Identify Results dialog.
You can think of all kinds of uses for actions. For example, if you have a point layer containing locations of images or photos along with a file name, you could create an action to launch a viewer to display the image. You could also use actions to launch web-based reports for an attribute field or combination of fields, specifying them in the same way we did in our Google search example.
We can also make more complex examples, for instance on how to use Python actions.
Usually when we create an action to open a file with an external application we can use absolute paths, or eventually relative paths, in the second case the path is relative to the location of the external program executable file. But what about we need to use relative paths, relative to the selected layer (a file based one, like a shapefile or spatialite)? The following code will do the trick:
command = "firefox"; imagerelpath = "images_test/test_image.jpg"; layer = qgis.utils.iface.activeLayer(); import os.path; layerpath = layer.source() if layer.providerType() == 'ogr' \ else (qgis.core.QgsDataSourceURI(layer.source()).database() \ if layer.providerType() == 'spatialite' else None); path = os.path.dirname(str(layerpath)); image = os.path.join(path,imagerelpath); import subprocess; subprocess.Popen( [command, image ] );
we have to just remember that the action is one of type Python and to change the command and imagerelpath variables to fit our needs.
But what about if the relative path need to be relative to the (saved) project file? The code of the Python action would be:
command="firefox"; imagerelpath="images/test_image.jpg"; projectpath=qgis.core.QgsProject.instance().fileName(); import os.path; path=os.path.dirname(str(projectpath)) if projectpath != '' else None; image=os.path.join(path, imagerelpath); import subprocess; subprocess.Popen( [command, image ] );
Another Python actions example if the one that allows us to add new layers to the project. For instance the following examples will add to the project respectively a vector and a raster. The name of files to be added to the project and the name to be given to the layer are data driven (filename and layname are column names of the table of attributes of the vector where the action was created):
qgis.utils.iface.addVectorLayer('/yourpath/[% "filename" %].shp','[% "layername" %]',\ 'ogr')
To add a raster (a tif image in this example) it becomes:
qgis.utils.iface.addRasterLayer('/yourpath/[% "filename" %].tif','[% "layername" %]')
The Joins menu allows you to join a loaded attribute table to a loaded vector layer. After clicking the Add vector join dialog appears. As key columns you have to define a join layer you want to connect with the target vector layer , a join field that corresponds to an attribute column in the target layer and a target field you find in the attribute table of the target vector layer here. As a result, all information of the join layer and the target layer are displayed in the attribute table of the target layer as joined information.
QGIS currently supports to join non spatial table formats supported by OGR (e.g. CSV, DBF and Excel), delimited text and the PostgreSQL provider (see figure_joins_1).
Figure Joins 1:
Additionally the add vector join dialog allows to:
The Diagrams menu allows you to add a graphic overlay to a vector layer (see figure_diagrams_1).
The current core implementation of diagrams provides support for piecharts, text diagrams and histograms.
The menu is divided into four tabs now: Appearance, Size, Postion and Options.
In the case of the text diagram and piechart text values of different data columns are displayed one below the other with a circle or a box and dividers. In the Size tab diagram size is based on a fixed size or on linear scaling according to a classification attribute. The placement of the diagrams which is done in the Position tab interacts with the new labeling, so position conflicts between diagrams and labels are detected and solved. In addition to chart positions can be fixed by the users hand.
Figure Diagrams 1:
We will demonstrate an example and overlay the alaska boundary layer a text diagram showing some temperature data from a climate vector layer. Both vector layers are part of the QGIS sample dataset (see Section Sample Data).
Figure Diagrams 2:
Remember that in the Position tab a Data defined position of the diagrams is possible. Here you can use attributes to define the position of the diagram. Also, a scale dependent visibility that you can find in the Appearance tab is possible.
In the Properties section you get general information about the layer, including specifics about the type and location, number of features, feature type, and the editing capabilities in the Properties section. The Extents table provides you with layer extent information, and the Layer Spatial Reference System information, providing information about the CRS of the layer. This is a quick way to get information about the layer.
Additionally you can add/edit a title for the layer and some abstract information in the Description. Also, it’s possible to define a Keyword list here. These keyword lists can be used in a metadata catalogue. If you want to use a title from an XML metadata file you have to fill in a link in the DataUrl field. Use Attribution to get Atrribute data from an XML metadata catalogue. In MetadataUrl you can define the general path to the XML metadata catalogue. These information will be saved in the QGIS project file for following sessions and will be used for QGIS server.
Figure Metadata 1: