Darkness becomes concentrated in the same way a planet takes shape. Gravity is already there, and so the raw elements begin the process of forming into a distinct form. Earth was formed by gravity, is subject to it, is arguably a manifestation of it, and has gravity of its own in a way.
The same process occurs with individuals. The Force is the gravity, with manifestations of all concievable shapes and sizes. Looking at the mythos for examples, most sentients within the universe had personal gravity akin to a Dovin Basal, enough to serve their limited purposes, which was usually determined by external forces with greater sentience (i.e. the Yuuzhan Vong).
Unlike dovin basals though, people have the potential to think for themselves, to possess and act on ambition, and to break away from notions of predetermined purpose. Those that possessed power had notably greater fields of gravity, encompassing entire worlds or systems of worlds, the range of which could fluctuate, grow drastically, or be snuffed out. Whereas common people could be compared to dovin basals, the powerful could be compared to the gravity of planets.
From smallest to largest spheres, examples – from, you guessed it, Star Wars 😉 – could range from slaves on some far away wasteland planet to senators in galaxy-spanning governments based off of Coruscant to Dark Lords of the Old Sith Empire like King Adas, Mark Ragnos, Naga Sadow, or even Freedon Nadd. A select few within the stories expanded their field of gravity, their sphere of influence, to encompass nearly the entire galaxy. Darth Sidious (aka Emperor Palpatine), Lord Vitiate, Darth Krayt…
(Written May 10th, 2012 // Unfinished & Abandoned)