Difference between bar graph and histogram
Pictograph is the way of expressing the data with the help of pictures. A key picture is used as unit which represents a number of concerned object. For example, the pictograph showing the numbers of cars sold by a company in different years is given below:
Here, the key is "1 image of car = 1000 cars".
Bar graphs are used to represent "categorical data", or the data that is categorized. For example, the b graph of money earned by a trader in the different months is given below:
Here, the different categories are different months which have no relation with each other.
On the other hand, histograms are used to show "continuous data", or the data that is distributed in small intervals within a certain range. For example, the histogram of number of students scoring the marks in a particular range is given below.
Here, the scored marks are distributed in the small intervals such as 0-10, 10-20, 20-30, 30-40 and 40-50 within the range of 10 marks.
Hope it helps!