GF:
The required gradient varies with number of engines. That is the minimum gradient to meet certification rules and applies even if departing over a cliff and the flight path is over the ocean w/o and obstacle in a thousand miles.
It's important to note that the operating rules (U.S. 121.189) require that the certification takeoff flight path (Part 25) be increased as necessary to avoid any obstacle that penetrates the certification surface and cannot be avoided laterally.
Also, there are the gross and net paths.