Area
a graph law graph shows the relationship between pressure and volume
A graph of Charles Law shows the relationship between temperature and volume of gas.
A line graph would show this.
A line graph shows change over a period of time.
The volume of gas
The volume of gas
A line graph shows changes (or trends) over time.
line graph
Area
If they are changes in time taking place, you use a line graph, but if they are changes in quantity taking place, you usea bar graph or a pie chart.
A graph of Charles' Law shows the relationship between Volume vs. Temperature. Volume is placed on the y axis and temperature on the x axis. The relationship is linear if temperature is in units of Kelvin.
This graph of Charles Law would show the relationship of volume of a gas as a function of the temperature at constant pressure.