Electrostatic Difference Potential, Hartree potential and contour plot

[nfizzati23]

Hi . I am trying to understand this three concepts based on the tutorial https://docs.quantumwise.com/tutorials/graphene_nanoribbon_device/graphene_nanoribbon_device.html.
So far, from previous question and answer i understand that EDP*e = -Hartree potential and  Hartree potential is based on electron density.
However, in the tutorial it said " to understand the effect of gate potential it can be seen from the contour plot". 
My question is how does gate potential affect the EDP? and is it correct that the contour plot shown in tutorial is hartree potential?

I hope someone can help me out. Thank you

[Petr Khomyakov]

EDP*e = -Hartree Difference potential (HDP), which is in units of eV. The plots refer to HDP (eV) as stated in the color bars.