When is a bargraph a better choice than a pictograph?

when displaying very small fractional or decimal values

Very small fractional or decimal values may appear unclear on pictographs. For example, it may be difficult to represent a value such as 0.018 or 1/16 using a picture of an object.

In a bar graph, however, the intervals can be chosen so that very small values are more clear. Also, tick marks and grid lines can be added to a bar graph to make it easier read such values.