What type of data representation involves ordering observations according to changes over time?

The correct answer is time series, which specifically refers to a sequence of data points that are collected or recorded at successive points in time. This type of data representation allows for the analysis of trends, patterns, and changes over time, making it particularly useful in various fields such as finance, economics, and environmental studies. By ordering observations chronologically, time series analysis can identify seasonal variations, cyclical patterns, and long-term trends, enhancing the understanding of how a variable behaves over different time periods.

In contrast, categorical data focuses on grouping observations into distinct categories without any inherent ordering over time. Numerical data tends to emphasize the quantitative aspects of data, while cross-sectional data represents observations collected at a single point in time, thus lacking the time component integral to time series analysis.