Why is it important for historians to create graphs from primary sources?

The correct answer to this open question is the following.

It is important for historians to create graphs from primary sources for the purpose of getting the information more clearly and visually so everybody can access the information a can understand it. A primary source is the one that was the product of people who witnessed the event or the incident. It could a testimony, a letter, an interview. So historians could create graphics to better explain the sequence of events, dates, and characters that participated in that part of history.

a primary source is a first hand source, it is usually from someone who was there at an event or experienced it

its important that they keep track of these sources, because when things are passed down, words get altered slightly every time they are retold (like the game telephone)

when they keep records of it, it prevents the actual events being messed with