"The site is nearby."
Translation:De locatie is dichtbij.
They are essentially the same, but vlakbij is a little closer than dichtbij, if you want to be specific. Vlakbij comes from vlak which means "flat" or "plane" - meaning on the same plane. Dichtbij comes from dicht which means thick, tight, dense or close. They are interchangeable but if you want to compare one to another, vlakbij is closer in Dutch.