Cytoscape_User_Manual/Visual_Styles

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What is a Visual Style?

One of Cytoscape's strengths in network visualization is the ability to allow users to encode any attribute of their data (name, type, degree, weight, expression data, etc.) as a visual property (such as color, size, transparency, or font type). A set of these encoded or mapped attributes is called a Visual Style and can be created or edited using the Cytoscape VizMapper. With the VizMapper, the visual appearance of your network is easily customized. For example, you can:

• Specify a default color and shape for all nodes.

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• Add any photo/image/graphics on the nodes.

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• Use specific line types to indicate different types of interactions.

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• Encode specific physical entities as different node shapes.

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• Set node sizes based on the degree of connectivity of the nodes. You can visually see the hub of a network...

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• ...or, set the font size of the node labels instead.

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• Set node widths and heights based on label size.

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• Visualize gene expression data along a color gradient.

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• Control edge transparency (opacity) using edge weights.

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• Control multiple edge visual properties using edge score.

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• Browse extremely-dense networks by controlling the opacity of nodes.

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• Show module locations in a large network.

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• Overlay a subnetwork on huge interactome using opacity and color control.

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Cytoscape 2.6.0 and later has additional sample Visual Styles. You can try those samples to understand how Visual Styles change appearence of a network. The following is a list of network views based on sample styles applied to galFiltered.sif network :

The VizMapper can be accessed by going to View → Open VizMapper or by clicking on the VizMapper icon . Also, starting in Cytoscape 2.5, direct access to the VizMapper is provided via a tab on the Control Panel at the left-hand side of the screen (formerly known as CytoPanel 1).

Introduction to the VizMapper User Interface

As of Cytoscape 2.5, the VizMapper has undergone a complete interface redesign. There are three types of components in the new VizMapper:

1. Main Panel

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   • This panel allows you to create/delete/view/switch between different visual styles using the Current Visual Style options. The Visual Mapping Browser at the bottom displays the mapping details for a given visual style and is used to edit these details as well.
2. Default Appearance Editor

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   • Clicking on the section labelled "Defaults" on the Main Panel will bring up this editor, which allows users to visually edit the default appearance of nodes and edges for the selected visual style.
3. Continuous Editors
   • These are editors for continuous mapping, which is a mapping from numerical value to visual attributes. They are accessed through the Visual Mapping Browser on the Main Panel. Using these windows, users can edit continuous mapping more intuitively.
   • Color Gradient Editor
   • Continuous-to-Discrete Editor
   • Continuous-to-Continuous Editor

These editors will be discussed in further detail below.

Introduction to Visual Styles

The Cytoscape distribution includes several predefined visual styles to get you started. To demonstrate these styles, try out the following example:

Step 1. Load some sample data

• Load a sample session file: From the main menu, select File → Open, and select the file sampleData/galFiltered.cys.

• The session file includes a network, some annotations, and sample visual styles. By default, galFiltered Style is selected. Gene expression values for each node will be colored along a color gradient between red and green (where red represents a low expression ratio and green represents a high expression ratio, using thresholds set for the gal4RGexp experiment bundled with Cytoscape in the sampleData/galExpData.pvals file). Also, node size is mapped onto the degree (number of edges connected to the node) and you can see the hubs of the network as larger nodes. See the sample screenshot below:

  

Step 2. Switch between different Visual Styles

You can change visual styles by making a selection from the Current Visual Style dropdown list (found at the top of the VizMapper Main Panel).

For example, if you select Sample1, a new visual style will be applied to your network, and you will see a white background and round blue nodes. Additionally, if you zoom in closer, you can see that protein-DNA interactions (specified with the label "pd") are drawn with dashed red edges, whereas protein-protein interactions (specified with the label "pp") are drawn with a solid light blue edge (see sample screenshot below).

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Finally, if you select Solid, you can see the graphics below:

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This Visual Style does not have mappings except node/edge labels, but you can modify the network graphics by editing Default View.

Additional sample styles are available as sampleStyles.props file in the SampleData directory. You can import the sample file from File → Import → Vizmap Property File.

Visual Attributes, Graph Attributes and Visual Mappers

The Cytoscape VizMapper uses three core concepts:

• A visual attribute is any visual setting that can be applied to your network. For example, you can change all nodes from circles to squares by changing the node shape visual attribute.

• A network attribute is any data attribute associated with a node or an edge. For example, each edge in a network may be associated with a label, such as “pd” (protein-DNA interactions), or “pp” (protein-protein interactions).

• A visual mapper maps network attributes to visual attributes. For example, a visual mapper can map all protein-DNA interactions to the color blue, and all protein-protein interactions to the color red.

Cytoscape allows a wide variety of visual attributes to be controlled. These are summarized in the tables below.

For each visual attribute, you can specify a default value or define a dynamic visual mapping. Cytoscape currently supports three different types of visual mappers:

1. Passthrough Mapper

   • The values of network attributes are passed directly through to visual attributes. A passthrough mapper is only used to specify node/edge labels. For example, a passthrough mapper can label all nodes with their common gene names.

2. Discrete Mapper

   • Discrete network attributes are mapped to discrete visual attributes. For example, a discrete mapper can map all protein-protein interactions to the color blue.

3. Continuous Mapper

   • Continuous graph attributes are mapped to visual attributes. Depending on the visual attribute, there are three kinds of continuous mappers:

     1. Continuous-to-Continuous Mapper: for example, you can map a continuous numerical value to a node size.

     2. Color Gradient Mapper: This is a special case of continuous-to-continuous mapping. Continuous numerical values are mapped to a color gradient.

     3. Continuous-to-Discrete Mapper: for example, all values below 0 are mapped to square nodes, and all values above 0 are mapped to circular nodes.

   • However, note that there is no way to smoothly morph between circular nodes and square nodes.

The table below shows visual mapper support for each visual property.

Legend

Node Visual Mappings

Edge Visual Mappings

Custom Graphics Manager

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From Cytoscape 2.8.0, Cytoscape supports Custom Graphics for nodes. You can add all kinds of bitmap images, such as jpg, png, or gif, on the top of network nodes. Conceptually, this is simply an addition to the Visual Properties, and you can use same VizMap user interface to map bitmap images to nodes. However, before mapping images, you need to prepare Custom Graphics in Custom Graphics Manager. It is a simple GUI component to add/remove images to Cytoscape session.

Adding New Images to Cytoscape

Removing Images

Use Custom Graphics in VizMap

Custom Graphics Selector

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Saving and Loading

When you quit from Cytoscape, all of the Custom Graphics in the manager will be saved automatically. There are two types of saving system:

1. Saving Custom Graphics to session
2. Automatic Saving

   • When you select File-->Quit, all of Custom Graphics in the Manager will be saved automatically to your Cytoscape setting directory.

Visual Styles Tutorials

The following tutorials demonstrate some of the basic VizMapper features. Each tutorial is independent of the others.

Tutorial 1: Create a Basic Visual Style and Set Default Values

The goal of this tutorial is to learn how to create a new Visual Style and set some default values.

Step 1. Load a sample network. From the main menu, select File → Import → Network (Multiple file types), and select sampleData/galFiltered.sif.

Step 2. Open the VizMapper. Select the View → Open VizMapper menu option, or select the VizMapper icon in the main button bar, or click on the VizMapper tab in the Control Panel at the left of the screen. You will now see a VizMapper Main Panel, as shown below.

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Step 3. Create a new visual style. Click the Options button, and select Create new visual style... Then enter a name for your new visual style when prompted. You will see an empty visual style in the VizMapper Main Panel, as shown below.

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Since no mapping is set up yet, all visual attributes are listed in the Unused Properties category. From this panel, you can create node/edge mappings for all visual properties.

Step 4. Edit default values. Open the Default Appearance Editor by clicking on the Defaults graphics window (shown below) in the VizMapper Main Panel.

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Step 5. Change the default node shape. To set the default node shape to triangles, click "Node Shape" in the Default Visual Properties list. A list of available node shapes will be shown. Click on the Triangle icon and then click the Apply button. The Default Appearance Editor will be automatically updated. You can edit other default values by clicking on visual attribute names on the list. In the example shown below, the node shape is set to Triangle, while the node color is set to blue.

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Step 6. Apply your settings. When you finish editing, click the Apply button at the bottom of the editor. Your new Visual Style will be applied to the current network, as shown below.

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Tutorial 2: Creating a New Visual Style with a Discrete Mapper

The following tutorial demonstrates how to create a new visual style using a discrete mapper. The goal is to draw protein-DNA interactions as dashed blue lines, and protein-protein interactions as solid red lines.

Step 1. Load a sample network. From the main menu, select File → Import → Network (Multiple file types), and select sampleData/galFiltered.sif.

Step 2. Open the VizMapper. Select the View → Open VizMapper menu option, or select the VizMapper icon in the main button bar, or click on the VizMapper tab in the Control Panel at the left of the screen.

Step 3. Create a new visual style. Click the Options button, and select Create new visual style... Name your new style “Tutorial VS2”.

Step 4. Choose a visual attribute. Double click the Edge Color entry listed in Unused Properties. Edge Color will now appear at the top of the list, under the Edge Visual Mapping category (as shown below).

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Step 5. Choose a network attribute. Click on the cell to the right of the Edge Color entry and select "interaction" from the dropdown list that appears.

Step 6. Choose a mapping type. Set the Discrete Mapper option as the Mapping Type. All available attribute values for "interaction" will be displayed, as shown below.

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Step 7. Set the mapping relationship. Click the empty cell next to "pd" (protein-DNA interactions). On the right side of the cell, ... and X buttons will appear. Click on the ... button. A popup window will appear; select blue, and the change will immediately appear on the network window.

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Repeat step 7 for "pp" (protein-protein interactions), but select red as the edge color. Then repeat steps 4 through 7 for the Edge Line Style attribute. You can select the correct line style (dashed or solid) from the dropdown list.

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Now your network should show "pd" interactions as dashed blue lines and "pp" interactions as solid red lines. A sample screenshot is provided below.

Tutorial 3: Visualizing Expression Data on a Network

The following tutorial demonstrates how to create a new visual style using a continuous mapper. The goal is to superimpose gene expression data onto a network and display gene expression values along a color gradient.

Step 1. Load a sample network. From the main menu, select File → Import → Network (Multiple file types), and select sampleData/galFiltered.sif.

Step 2. Load sample expression data. From the main menu, select File → Import → Attribute/Expression Matrix, and select sampleData/galExpData/pvals.

Step 3. Open the VizMapper. Select the View → Open VizMapper menu option, or select the VizMapper icon in the main button bar, or click on the VizMapper tab in the Control Panel at the left of the screen.

Step 4. Create a new visual style. Click the Options button, and select Create new visual style... Name your new style “Tutorial VS3”.

Step 5. Choose a visual attribute. Double click the Node Color entry listed in Unused Properties. Node Color will now appear at the top of the list, under the Node Visual Mapping category.

Step 6. Choose a network attribute. Click on the cell to the right of the Node Color entry and select "gal1RGexp" from the dropdown list that appears.

Step 7. Choose a mapping type. Set the Continuous Mapping option as the Mapping Type. This automatically creates a default mapping

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Step 8. Define the points where colors will change. Double-click on the black-and-white gradient rectangle next to Graphical View to open the Color Gradient Mapper. Click and drag one point to -1, or type the value in the Range Setting box. Set the second point to 2.

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Step 9. Define the colors between points. Double-click on the leftmost triangle (facing left) and a color palette will appear. Choose a shade of yellow and click OK. Double-click on the triangle at -1 and set the color white. For triangle at 2, set its color to red. Set the rightmost triangle to black.

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The color gradients will immediately appear in the network window. All nodes with a gal1RGexp value less than –1 will be set to yellow, and all nodes with a gal1RGExp value greater than 2 will be black. Additionally, all values between –1 and 2 will be painted with a white/red color gradient. A sample screenshot is below.

Tutorial 4: How to Use Utilities for Discrete Mappers

The following tutorial demonstrates new features in Cytoscape 2.5. The new VizMapper user interface has some utilities to help users editing discrete mappings. The goal of this section is learning how to set and adjust values for discrete mappings automatically.

1. Load a sample network: From the main menu, select File → Import → Network, and select sampleData/galFiltered.sif.

2. Apply layout to the network: From the main menu, select Layout → Cytoscape Layouts → Degree Sorted Circle Layout. This layout algorithm sort nodes in a circle by degree of the nodes. Degrees will be stored as node attribute names Degree after you applied this algorithm.

3. Click the VizMap button on the tool bar.

4. Click Defaults panel on the VizMapper main panel. Default Apearence Editor pops up (see below.)

5. Edit the following visual properties and press Apply. Since you changed opacity of the node, you can see the nodes bihind the front node (see below.)

   • Node Oppacity - 100
   • Edge Color - White
   • Background Color - Black

   

6. Cretate a Discrete Node Color Mapping. Select Degree as controlling attribute.

7. Select Node Color, then right click to show popup menu. Select Generate discrete values → Rainbow 1. It generates different colors for different attribute values as shown below.

   

8. Cretate a Discrete Node Size Mapping. Select Degree as controlling attribute.

9. Select Node Size and right click to show popup menu. Select Generate Discrete Values → Series (Numbers Only). Type 30 for the first value and click OK. Enter 15 for increment.

10. Apply Force-Directed layout. Final view of the window looks like the following.

    

Advanced Topics

Editing Discrete Mappings

From version 2.5, several utility functions are available for Discrete Mappings. You can use those functions by right clicking anywhere on the Visual Mapping Browser (shown below.)

Automatic Value Generators

• Generate Discrete Values - Functions in this menu category are value generator for discrete mappings. Users can set values for discrete mappings automatically by these functions.

  • Rainbow 1 and Rainbow 2 - These functions try to assign as different colors as possible to each values. see the example below:

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  • Randomize - Randomize colors and numbers. If you use this function for numerical values (node size, opacity, etc.) you need to specify a range. For example, if you want to set values from 1 to 100, you need to type 1-100 in the dialog.

  • Series - Set series of numbers to the specified mapping.

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  • Fit node size to label - This function is only for node width and height. When node size is unlocked AND Node Width/Height discrete mappings are available, you can fit the size of each node to label automatically by selecting this function. See the example below:

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• Modify Discrete Values - Currently, this is only for colors. You can change overall brightness for discrete color mappings.

Edit Selected Values at Once

You can set multiple values at once. First, you need to select rows you want to change values then select Edit selected values at once.... A dialog pops up and you can enter the new value for the selected rows.

Visual Property Dependencies

The fourth pane in the Default Editor lists available dependencies that can be established between different visual properties. The two that currently exist are Lock Node Width/Height and Make Arrow Color Match Edge Color.

• Lock Node Width/Height - If this menu item is checked, Node Width and Node Height mappings are ignored and Node Size overrides them. If you want to use Fit node size to label function, you need to unlock this.

• Make Arrow Color Match Edge Color - If this menu item is checked then Edge Source Arrow Color and Edge Target Arrow Color are overridden and Edge Color is used in both cases.

Working with Continuous Mapping Editors

There are three kinds of Continuous Mapping Editors. Each of them are associated with a specific visual attributes:

Range Setting Panel

Each editor has a common section named Range Setting.

1. Handle Value Box - This box displays current value for selected slider handle. Also you can directly type value in this box to move the slider to exact location.

2. Min/Max Button - Set the overall range of this editor. First time you open the editor, the Min and Max values are set by the range of attribute you selected, i.e., minimum and maximum value of the attribute will be set to the range of this editor. You can change this range anytime you want by pressing this button.

3. Add Handle Button - Add a new handle to the editor.

4. Delete Handle Button - Delete selected handle from the slider widget.

Gradient Editor

Gradient Editor is a editor to create continuous mapping for colors. To change the color of each region, just double click the handles (small triangles on the top). Color gradient will be created only when editor has two or more handles (see the example below).

Continuous-Continuous Editor

Continuous-Continuous Editor is for creating mapping between numerical attributes and numerical visual properties (size/opacity). To change the value assigned on Y-axis (visual property shown in the example above is node size), drag the red squares or double click on the squares to directly type exact value.

Continuous-Discrete Editor

Continuous-Discrete Editor is used to create mapping from numerical attribute values to discrete visual properties, such as font, shape, or line style. To edit a value for specific region, double click on the icon on the track.

Managing Visual Styles

All Cytoscape Visual Style settings are initially loaded from a a default file called vizmap.props that cannot be altered by users. When users make changes to the visual properties, a vizmap.props file is saved in the session file. This means that assuming you save your session, you will not lose your visual properties. No other vizmap.props files are saved during normal operation.

Saving Visual Styles

Visual styles are automatically saved with the session they were created in. Before Cytoscape exits, you will be prompted to make sure you save the session before quitting. It is also possible to save your visual styles in a file separate from the session file. To do this, navigate to the File → Export → Vizmap Property File menu option and save the properties as a file. This feature can be used to share visual styles with other users.

Importing Visual Styles

To import existing visual styles, navigate to the File → Import → Vizmap Property File menu option and select a vizmap.props file. Imported properties will supplement existing properties or override existing properties if the properties have the same name. You can also specify a visual properties file using the -V command line option (cytoscape.sh -V myVizmap.props). Visual properties loaded from the command line will override any default properties.

Default Visual Styles

It is possible to change the default visual properties for all sessions of Cytoscape. To do this, navigate to the Edit → Preferences → Properties... menu option, check the "Make Current Visual Styles Default" box in the Default Visual Styles section, and click the OK button. This will save the current visual styles as a vizmap.props file to your .cytoscape directory (found in your home directory). These visual styles will then be loaded each time Cytoscape is started.

Bypassing Visual Styles

Cytoscape has a feature that allows users to override visualizations created by the VizMapper for individual nodes and edges. This feature is available by right-clicking on a node or edge and then clicking on the Visual Mapping Bypass menu.

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Each visual property of the node or edge is displayed. When a property is overridden, a checkmark appears next to the property and a [Reset <Property Name>] menu option appears directly below it. By clicking this Reset option, the bypass will be removed and the attribute will be displayed as defined by the VizMapper. At the bottom of the menu a Reset All option appears. When clicked, this will remove all bypasses for the specified node or edge. In the example above, you can see the selected node size, color, and shape have been overridden. This is apparent in the appearance of the node itself and by the check marks in the popup menu.

It is important to realize that the Visual Mapping Bypass only works for individual nodes and edges and not for all nodes or edges of a specific type. Using the bypass function is not particularly resource intensive, meaning you can use it as much as you like. However, if you ever find yourself repeating the same bypasses, then you should consider using the VizMapper instead.

Bypass is accomplished using special attributes with names like node.fillColor and node.shape. These are normal Cytoscape attributes and can be seen and edited in the Attribute Browser. The value of the attribute is a string representation of a property. For example, color is represented by 3 integers representing the RGB (red, green, blue) value of the color. Different types of properties have different string representations. When in doubt, just use the right click menu to create valid attribute values.

Because bypass values are specified using normal attributes, these attributes will persist between sessions only as long as you save your session! If you don't save your session, you will lose whatever bypass values you set.

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