What is represented by the distance between two vertical white gridlines on this graph?

• A. A time span of 50 years
• B. A time span of 10 years
• C. The population size
• D. An age category

Answer: (A)

On this graph, the horizontal axis represents time in years, and the vertical white gridlines fall at regular time intervals. The spacing between neighboring gridlines is a fixed time increment, and in this graph that increment corresponds to 50 years. So the distance between two vertical gridlines represents 50 years. This is about how the axis is scaled, not about population size or age categories, which would be shown by different labels or data, not by the gridline spacing.