# Is a line considered a face in graph theory?

Is a line considered a face in graph theory?

For example just a straight line point to point.

0-------------------------0

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Please try to make your titles more descriptive. Almost all your questions are titled "<Branch of Math> Question". –  Austin Mohr Feb 20 '12 at 2:00

No, that is an edge. There is one face in your graph though: the unbounded or infinite face, sometimes denoted $f_\infty$.
The degree of $f_\infty$ in this case is 2, since your walk uses the edge twice to return to the starting vertex. Note that the sum of all the degrees of the faces in a planar graph is always twice the number of edges. –  Zach Langley Feb 20 '12 at 2:39