Relative frequencies of class intervals also can be shown in a frequency polygon. In this chart, the frequency of each class is indicated by points or dots drawn at the midpoints of each class interval. Those points are then connected by straight lines.
Comparing the frequency polygon (shown in Figure 1) to the frequency histogram (refer to Figure 1 in "Frequency Histogram"), you see that the major difference is that points replace the bars.
Figure 1.Frequency polygon display of items sold at a garage sale.