Whether we notice it or not, many things change over time. If we want to understand the degree of change and how meaningful it was, we can visualize it on a chart.

Air temperature is something that changes over time. Knowing today's temperature doesn't guarantee that tomorrow's temperature will be the same; temperature can change quickly, from day to day and hour to hour. However, we can look at temperature data from the last week, month, or year and get an idea of what to expect in a general way.

In this chapter, we will use a visualization of a specific type of data to assess how something changes over time. We call this type of data a “time series”.