Line-chart based on a histogram
, it is drawn by joining the mid-points of the blocks at their apexes with a straight line. The extreme points of the line are joined to the horizontal ('X') axis (where the mid-point of the respective next class
would have been) to result
into a polygon
. In a very large set of data
(where the number of classes increases and difference between their widths decreases) the polygon turns into a smooth curve known as frequency
curve or frequency distribution
curve. Histographs (and histograms) are commonly used where the subject item is discrete
(such as the number of students in a school) instead of being continuous (such as the variations in their heights).
Also called frequency polygon
, a histograph is usually preferred over histogram where the number of classes is eight or more.