Starcraft – Forming an arc in SC2 – mechanics

starcraft-2

In this question:

Forming a "concave" with your army

We get a nice explanation of why we want to form arcs with our armies. What I'm wondering is how to actually do it, in terms of commands. Two ways I know of:

  • Moving your whole army perpendicular from the opposing forces until they form an arc, then hitting 'Hold Position'.
  • Boxing and spreading units manually.

Is there an easier way, maybe with multiple control groups and/or hold/patrol commands? How are the top players forming their arcs?

Thanks!

Edit

The reason I use "Hold" to form my arcs is because a line is formed when you run your units as far as their sizes combined. If you simply 'Move' to the position, you will bunch up into a ball. I guess I can try 'Stop' for this instead like has been suggested, but what I'm really hoping for is more along the lines of Budda's answer of using 3 control groups (maybe even pre-split with N marauders, N marines, and N/4 medivacs). I'm going to leave the question open for a little while longer just to make sure we're not missing anything.

Edit 2

Sadly, it appears that positioning units manually is the best arc forming method. I still find myself using patrol to send units north, shift-move them just a few steps south of the north rally point, and then shift-move to where I want to go (further north in this example) to get a better arc (YMMV). I chose the more general answer even though I may have liked the other answer better because I think it will better fit users coming in from Google. Thanks again.

Best Answer

"Hold position" actually is a generally bad thing for forming arcs. Your units will automatically move to form an arc when engaging in a fight.

A simple example is attacking destructible rocks. When you attack them, your army automatically arcs around the rocks. You will see units automatically stop and attack as soon as they are in range of the rocks. Units that are out of range and are blocked by other attacking units will sort of "peel" off the back layer into the edges of the arc shape.

In general, automatic attack behavior will form the ideal arc. But there are a few things to consider still in making the arc formation as quick and efficient as possible:

  1. Positioning. Give your army room to spread, and keep your opponent in a choke. Either by using map features, buildings, or by Protoss force fields
  2. Before the engagement, try to keep your units in a position which will allow them to form a quick arc:
    1. Keep them in a line roughly in the shape of the arc. It can be very approximate.
    2. "Holes" in this line are a good thing, so units in the back can filter easily to the front without having to move far.
    3. Units with less range go in the front. Melee units especially... watch a Protoss battle where zealots are behind stalkers and you'll see how worthless they are (and if Protoss has blink, he will often blink stalkers behind the zealots at the start of an engagement).
  3. If you have blink stalkers, you can blink some stalkers to the side a bit to form an instant arc.
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