"A desire line map shows the sum of all the straight lines connecting the origins and the destinations of all trips. The desire line is the shortest line between origin and destination, and expresses the way a person would like to go, if such a way were available" (cited in Throgmorton & Eckstein, c1999).
Sometimes desire lines can be rather beautiful or even intriguing: like this X-marks-the-spot I spotted in Tromsø in northern Norway.
Throgmorton, James & Eckstein, Barbara (c1999) Desire Lines: The Chicago Area Transportation Study and the Paradox of Self in Post-War America, accessed 15/08/2011 at, http://www.nottingham.ac.uk/3cities/throgeck.htm
Burch, Stuart (2011) "Paths of undesire", blog posting, 17/08/2011, available at, http://www.stuartburch.com/1/post/2011/08/paths-of-undesire.html
At my place of work there was once a series of desire paths snaking their way between various buildings. Rather than trying to prevent their use, my employer has made the sensible decision to make them official. What was once trampled-down grass is now a neat asphalt route. Permanent desire, in other words!