# Adding an Additional Axis to a Plot

**QUESTION:** What is the best way to add a second, logarithmic axis to my line plot?

** ANSWER:** An additional axis can be added to a plot with the **cgAxis** command. Be sure you set the **Save** keyword when you use the command, so that the subsequent overplotting of data will use the proper axis scaling.

Here is IDL code that plots a damped sine curve on a normal, linear Y axis and logarithmic data on a second, logarithmic axis. Click here to download a more complete code example.

x = Findgen(100) theta = x/5 curve = Sin(x/5) / Exp(x/50) ; Plot the damped sine curve. Suppress drawing the right-hand Y axis. cgPlot, curve, YStyle=8, Color='red7' ; Draw a second, logarithmic axis on the right-hand side of the plot. cgAxis, YAxis=1, YLog=1, YRange=[0.1, 100], /Save ; Overplot the logarithmic data. cgOplot, theta, Color='blu7'

Here is an illustration of the plot produced by the IDL code above.

Last Updated 26 July 2013