The trend tool lets you see data across time. You may add multiple geographies to the chart for a chosen indicator.
The average and high / low values will apply to the geography type of the first geography in the list.
So if a city is listed first and a county is added below it, the chart will show the average & high / low of cities.
The trend tool only shows indicator data from the same source, which is why the indicator selection is limited in comparison to the profiles and compare tool.
The compare tool lets you compare geography data side by side. You may add multiple indicators to compare side by side.
You can also add up to 5 geographies to compare against each other. The compare tool has a variety of chart types to help visualize the data.