An interval on a graph is the number between any two consecutive numbers on the axis of the graph. If one of the numbers on the axis is 50, and the next number is 60, the interval is 10. The interval remains the same throughout the graph.
The interval begins at any number that makes sense for representing the data on the graph. The size of the interval affects the visual impact of the graph. Using different intervals can make the same information appear different when applied to a graph. A large interval results in a short and wide graph, whereas a small interval produces a tall graph.