Visualization tab: Difference between revisions

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Additionally, some methods are constrained by additional or different objectives:
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 [[#centrality layout|concentric circles]] or [[#status layout| verical layers]] corresponding to the attributes values.
* node placement is restricted with respect to a given scalar node attribute, e.g., such that nodes lie on [[#centrality layout|concentric circles]] or [[#status layout| verical layers]] corresponding to the attributes values.
* the layout should ease comparison with respect to the previous layout, given a [[#dynamic layout|sequence of networks]].
* given a [[#dynamic layout|sequence of networks]], the layout should ease comparison with respect to the layout of the previous network in the sequence.
* the layout should reveal [[#spectral layout|specific structural properties]].
* the layout should reveal [[#spectral layout|specific structural properties]].


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==== random layout ====
==== random layout ====


=== link routing ===
=== link routing ===

Revision as of 13:33, 12 April 2011

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:


stress minimization

Stress minimization is our preferred method to obtain a layout for general 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.

Stress minimization is an instance of a family of dimension-reduction techniques referred to as multidimensional scaling (MDS).

metric MDS

centrality layout

status layout

dynamic layout

stress minimization (dyad attributes)

spring embedder

spectral layout

circular layout

random layout

link routing

...


label placement

...

mapping

color

size

label

coordinates

z-layer

geometry

affine transformations

...

procrustes analysis

...