Dear all,
Yesterday, I looked at a map of the metro in Barcelona, and I came to think about whether we could learn something from such maps when producing graphs for graphical models. (With many variables, a graphical model tends to look "messy").

Edges in metro-maps are often not straight lines - they tend to be composed of line segments forming 0, 45 and 90 degrees angles relative to some coordinate system - and that really makes the maps easier to look at. Have anyone looked at this idea? (It is not a particularly original idea so I guess the answer is "yes"!) 

It should be reasonably straight forward to formulate a heuristic for creating such edges: 1) The length of an edge should be small under the constraints that, 2) there is a "low price" on horisontal and vertical line segments and 3) a "high price" on 45-degree, 135 degree and so on lines. The actual shape of an edge under such requirements is not unique, for example the lines 
o--       o-
   \        \        .......
    --o       ---o
will have the same "price" - so some heuristic is needed to choose one from another. 

Comments, ideas, references??

Best regards
Søren

============================================================================================= 
Søren Højsgaard,  MSc, PhD (Statistics),        Phone: +45 8999 1703 
Head of Biometry Research Unit,                 Fax:     +45 8999 1300 
Danish Institute of Agricultural Sciences       E-mail: sorenh@agrsci.dk 
Research Centre Foulum, DK-8830 Tjele, Denmark  Homepage : http://www.jbs.agrsci.dk/~sorenh/ 

.... Time flies like an arrow, fruit flies like a banana ....

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