For showing changes in a city's population size over time, the best visual aid would be a **line graph**. Here's why:
1. **Trend Visualization:** Line graphs are ideal for illustrating trends and changes over time. By plotting the population size on the y-axis and time on the x-axis, you can easily see how the population has increased or decreased across different time periods.
2. **Easy Comparison:** A line graph allows for a clear comparison between different points in time. This makes it simple to identify periods of significant population growth or decline, providing a comprehensive overview of the city's demographic changes.
3. **Data Interpretation:** Line graphs help in interpreting the data effectively. Patterns, fluctuations, and overall population trends can be easily identified and understood through the visual representation of the data points connected by lines.
In summary, a line graph is the most suitable visual aid for showing changes in a city's population size over time due to its ability to visualize trends, facilitate comparison, and aid in data interpretation effectively.
