Resistors scaling in voltage divider?
You are trying to create an adjustable voltage power supply? I'm sorry to say that this design will not work. As you read, the output impedance (also called output resistance) will be very high. 

There is a certain amount of current that goes through the voltage divider resistors in your circuit (ignoring the output), which you can calculate using Ohm's Law. The current that you want to supply through the output must be much less than the current through the resistive divider.

For example, if you have a simpler voltage divider (to divide by 2) of 10k and 10k, the current from a 30V supply will be \$I = \frac{30\text{ V}}{20\text{ k}\Omega} = 1.5 \text{ mA}\$. It will not be able to supply anything close to 1.5 mA without the voltage dropping toward 0 V.