Visualization tab

Visualization algorithms change the graphical appearance of the network; they are accesible via the visualization tab. Basic illustrations of how to layout networks or display attribute values are provided in the two trails on visualization and analysis and advanced attribute management.

visone distinguishes between three major visualization categories

• layout to recompute the positions (coordinates) or nodes, links-bends, or labels to optimize readability or other specified layout criteria;
• mapping to specify how attribute values (such as node centrality, tie strength, or class membership) are encoded in grapical variables (such as size, width, or color);
• geometry to apply geometric transformations such as rotation, reflection, or scaling to the network or parts of the network;

layout

Layout refers to the task of obtaining positions for the elements of a network visualization, where computing node positions is of primary interest. Other tasks are (re-)routing the links of a visualization, e.g. to avoid overlap between link and node representations, or to automatically arrange label positions for better readability.

node layout

The methods in this section deal with the computation of node positions for one or more networks. Generally, nodes are considered to be geometric points (or objects that are described by a single point), and links are represented as straight lines between their incident nodes. Thus, most methods produce so called straight-line drawings (also referred to as node-link diagrams or sociograms).

There are several general objectives that most methods try to optimize, such as:

• links should have more or less the same length.
• nodes should be distributed well over the drawing area.
• the number of meaningless link crossings should be kept small.
• structural symmetries in the network should be represented well.

Additionally, some methods are constrained by additional or different objectives:

• node placement is restricted with respect to a given scalar node attribute, e.g., such that nodes lie on concentric circles or verical layers corresponding to the attributes values.
• given a sequence of networks, the layout should ease comparison with respect to the layout of the previous network in the sequence.
• the layout should reveal specific structural properties.

stress minimization

Stress minimization, an instance of a family of dimension-reduction techniques referred to as multidimensional scaling (MDS), is our preferred method to obtain a general-purpose layout for networks. The main idea is to compute a layout such that graph-theoretic distances (i.e., shortest-path lengths) between nodes are represented as good as possible, where more weight is placed on representation error with respect to shorter distances than larger ones. The method usually meets the general criteria mentioned above, and yields better results than spring embedders in most cases.

Note that the outcome of stress minimization is dependent on the current layout of the network. We suggest to compute a metric MDS layout first to obtain good results. Also note that computing a layout via the quick layout button corresponds to this procedure, i.e., applying stress minimization to a metric MDS layout.

For more details on the options available in visone, see the concept page for stress minimization.

link routing

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label placement

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geometry

affine transformations

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procrustes analysis

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