Frequency polygon

A frequency polygon carries the same information as a histogram but draws it as a single line, which makes two distributions easy to overlay on one set of axes. Each point sits above the midpoint of a bin, at a height equal to that bin's frequency. For example, a bin covering 60 to 70 that holds 8 values contributes the point $(65, 8)$, because the midpoint is $(60 + 70) / 2 = 65$. The line is usually anchored down to zero at an empty bin on each end so the polygon closes onto the axis.