Interval Visibility Graphs
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Consider a vertical stack of open intervals, such as , , , . Two intervals are said to have vertical visibility if a vertical line can be drawn between two intervals without intersecting some other interval.[more]
Graphs can represent interval visibility by mapping horizontal intervals to vertices and vertical lines to edges. All such graphs must be planar.
These are frequently called bar visibility graphs.[less]
Contributed by: Ed Pegg Jr (September 2015)
Open content licensed under CC BY-NC-SA
 Y. Chang, J. P. Hutchinson, M. S. Jacobson, J. Lehel, D. B. West, "The Bar Visibility Number of a Graph," SIAM Journal on Discrete Mathematics, 18(3), 2004, pp. 462–471. http://www.math.illinois.edu/~dwest/pubs/visno.pdf.
 M. Axenovich, A. Beveridge, J. P. Hutchinson, and D. B. West, "Visibility Number of Directed Graphs," SIAM Journal on Discrete Mathematics, 27(3), 2013 pp. 1429–1449. www.math.kit.edu/iag6/~axenovich/media/visibility.pdf.
"Interval Visibility Graphs"
Wolfram Demonstrations Project
Published: September 29 2015