Seok-Hee Hong Damian Merrick Hugo A. D. do Nascimento The Metro Map Layout Problem. 482-491 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3383&spage=482 2004 conf/gd/2004 Graph Drawing db/conf/gd/gd2004.html#HongMN04