As asked shall go a little bit more indepth, it alters with each time since we run it very loose but it basically goes like this.
DM: "As you enter the alleyway you notice a group of Ravagers (think voodoo possessed Gnoll zombies) at the far end of it."
*Rolls Initiative*
DM: "Two of the Ravagers draw near to you, the putrid smells of their body filling the air around you. Too the Gnolls left beside him is a rickety balcony its beams rotten"
P1: "I close in near the Ravager and smash it into the wall beside him." (Power be used that pushes the target).
Essentially we use these certain terms to describe the distance instead of using meters/squares. I trust my players and they trust me, so if they say that their power pushes the target near or far, or they can draw near, beside, far, etc. Then that is what happens and vice-versa.
Along the way I use the same terms to describe the surroundings, so the surroundings evolve and change as the battle progresses. Hell I may have something I didn't imagine to be there be imagined by a player or I think up on the fly.
I know that isn't really that indepth, but it is hard to go indepth when it is really run in a very simple manner. Essentially just based off of trust between what the DM and Players say as being so.
One thing I do, do to keep the mental map in my mind is have each monster's name on a piece of paper. Then draw a line with 3 markers on it: Beside, Near, Far. On this I place a movable prop that represents each PC, thus I can quickly glance to tell how far away each monster is from another PC (and thus how close they are from eachother as well).