2. Problem model
2.2 Visualization media representation
In current digital systems, visualization is usually made over two-dimensional media. Pictures are composed of patterns of pixels (picture elements). Although the configuration of the pixels can be constructed in an arbitrary fashion, they are normally represented as lattices of squared cells.
By considering the neighborhood of each pixel, modelling a connected pattern with a graph is straightforward. Calling this graph 
and using the definitions presented earlier, we can introduce the following elements:
As an extra definition, we introduce the characteristic 
of a pixel 
:
.
Cyberspace geography visualization - 15 October 1995
Luc Girardin, The Graduate Institute of International Studies
and their connections 
: 
,
: 
,
: 
,
: 
,
: 
,
and 
: 
.