Rotating Pace Line
Take that same basic paceline and add more rotation to it and it is called a rotating paceline. This is the second most popular type of paceline in cycling. The riders rotate to the front in a faster lane and rotate to the back in a slower, resting lane. The direction of the rotation is determined by the direction of the wind. If there is no wind it doesn't matter which way the lanes rotate. But as a rule of thumb, the resting or slower lane is used to block the wind from the progressing, faster line. If the wind shifts, the direction of the rotation will also switch.
Usually, in group-rides, I see a version of this that only rotates in one direction. So sometimes the entire group is fighting the wind up the progressing lane of riders. It makes no sense to do that!
More: Basic Skills for Group Riding
Other considerations to switch the rotation could be the type of shoulder on the road, room on the shoulder, or road hazards on the shoulder. The most important though to consider and to always keep in mind will be the wind, and you can track this by watching the grass, the trees or the occasional flag.
Echelon
An echelon is taking that same rotating paceline and extending it at an angle across the road depending on the direction of the wind. This typically can't be done in heavy traffic because of the space needed to use this paceline effectively. The purpose of an echelon is to keep a pace at a constant speed through the progressing lane while still blocking most of the crosswinds. This formation kind of looks like a wedge of riders at the front of a peloton, or a paceline not in a straight line but angled across the road.