The reason the wise general conquers the enemy is foreknowledge. -Sun Tzu
Scouting
Elements
Why scout?
How do I scout?
Where do I scout?
When do I scout?
What do I do with scouting information?
Why scout?
Knowledge is power!
The perfect strategy: one which adapts to the strategy of the opponent by striking its weaknesses and avoiding its strengths.
As in poker, information in StarCraft is not complete, and requires investments to narrow down the range of what the opponent could be up to. Scouting is not passive, rather it requires active map awareness and camera management.
There are many valid and effective ways to scout, so the methods you choose should compliment your preferred approach to the game.
How do I scout?
From low to medium to heavy investment
Procedure
Minimum investment
Soft Scouting: The cheapest scouting approaches have the lowest potential to damage your opponent. Overlords, overseers, scans, hallucinated phoenixes excel and getting information but won’t be killing anything.
Medium investment
Harassment scouting: At a more substantial expenditure, your scouting force can kill a few workers, knock out a building, and force a defensive reaction out of the opponent. A banshee or two, overlord drop, medivac drop, oracle, swarmhosts, and archon prism will cause the enemy to show you what they’re working with.
Heavy investment
Scouting with a big attack: Unleash a massive force at the opponent, and they’ll need to represent strong defense or face consequences such as losing a base, their production, or their army. Muta flocks of 15+, Terran doom drops, timing attacks, and mass oracle are examples of the most expensive ways to know exactly what the enemy is doing.
Where do I scout?
Filling vision: StarCraft maps tend to be large, so knowing where to prioritize your scouting efforts increases the efficiency of your investments in gaining information. Using the minimap as your regular reference, you want to keep tabs on the following:
Number of enemy bases
Location of enemy army
Type of enemy production facilities
Presence of gas-mining workers at their bases
Exits from enemy base
Entrances to your base
Dead space
When do I scout?
Knowing the gameflow: Scout timings are based on key decisions involving the development of economies, construction of production, training of forces, and their movement on the map. Understanding the gameflow allows you to make more accurate predictions when working with partial information. Much of deciding when to scout depends on your build, preferred playstyle, and confidence in defending attacks.
Worker scouting: 0:00-1:00
First overlord: 1:45-2:00
Reaper: 2:30-3:30
Adept: 2:40→
Oracle: 3:30→
2 base read: 4:00, 5:00→
3 base read: 7:00
Late game scouts 10:00, 15:00→
What do I do with scouting info?
Scouting doesn’t necessarily tell you everything, but can rule out possibilities and narrow down the range of what the opponent is going for. Identifying an attack means you can prepare forces to defend when it arrives, or counter attack as it is moving out. Discovering the tech investment will tell you their approximate unit composition, allowing you to craft a reasonably good counter. Knowing the location of the enemy army opens up opportunities to flank, surround, or circumvent their advance. Scouting informs your decision-making by giving you more evidence upon which to determine your next actions.