Having a scouting pillar for Overlord is considered one of the unspoken rules in modern map design. Does the scouting pillar affect the outcome of the game? This article examines this question.
This article is inspired by a post on reddit. The scouting pillar is the high ground outside of the natural expansion that allows Overlord to provide vision (see image below).
It is a common feature in modern competitive maps. The main purpose of the scouting pillar is to provide a safe position for the Overlord to park outside the opponent’s natural, so the Zerg player could have vision of the natural. This allows the Zerg player to send the Overlord into the opponent’s base at the optimum time for scouting. As highlighted by the author of the reddit post, Wardi’s comment in the video below sums up the perceived implications of the scouting pillar.
The author looked at the win rate across different maps descriptively and concluded that the scouting pillar has no effect on the match outcome. While I believe the question is interesting, the analysis has much room for improvement. For instance, any suitable multivariate analysis would provide better insight than the descriptive statistics alone. With this in mind, I decided to revisit this question with Ben, who has previously co-authored the article about the hidden side of GSL tournament format. He did all the tedious work with data and statistical analyses. All
hate credits go to him.
Does scouting pillar affect the Zerg match ups? If so, how?
We did not have specific predictions. I personally would expect the presence of pillars to favour Zerg slightly.
We only considered non-mirror 1v1 games with Zerg that were played during Legacy of the Void, starting with balance patch 3.8 (implemented December 2016) to 5.0.2 (August 2020). Expanding our sample beyond the current patch to include games over close to 3 years does not just enlarge our sample size, but it also helps to minimise the influence of exogenous variables in the statistical models (e.g., patch, metagame trend, and other map features). This would allow us to better capture the effect of the scouting pillar on match outcome.
We collected data from sc2replaystats. Sc2ReplayStats is a Starcraft 2 Replay Hosting/Training System based around Custom Statistics. The dataset includes 5,239,543 games using 70 unique maps over 13 balance patches: 3.1.1 to 5.0.2. They range from all skill levels and are user submitted games. It includes games played in all regions and the gamut of Bronze to GM. Games that ended in ties or without definitive wins and losses were omitted. After filtering for Zerg games, we are left with a total of 3,572,576 ZvT and ZvP games.
Balance patch 4.1.4 has problematic data because it ran for less than two months before 4.2.1 was then released. Rows with less than 100 games played were also removed, so they don’t disproportionately affect proceeding calculations.
We initially categorised the maps into “no pillar”, “pillar can see the entrance of the natural”, and “pillar cannot see the entrance of the natural”, but we decided to combine the “no pillar” and “pillar cannot see the entrance of the natural” into a single “no pillar” category. This is because of the low number of submissions for “pillar cannot see the entrance of the natural”. Logically, if the benefit of the pillar is to provide vision for the Zerg as argued by many, then “pillar cannot see the entrance of the natural” should be treated as “no pillar” instead of “pillar can see the entrance of the natural”.
Furthermore, we wanted to study whether there was a pillar effect over time or over patches, but the number of maps without pillars lessened over time.
2017: 7 of 20 maps did not have pillars
2018: 6 of 24
2019: 3 of 19
2020: 1 of 18
Four maps in the past 2 years and 4 balance patches does not provide enough of a sample to fairly compare sample sizes. It is worth pointing out that there are notably more maps with pillars than without pillars (2,911,923 vs. 660,653). Only two in the top 15 most played maps do not have pillars, and this reflects players’ veto preferences.The data also suggests that maps without pillars were becoming less common over the years.
The table below sums up the win rate of Zerg for non-mirror Zerg games.
At first glance, the win rates appear to suggest that the scouting pillar has no effect on win rate in both match-ups because they are very close to 50%. However, given our hypothesis, 50.45% was used instead of 50% as the base win rate, because we are comparing whether having the pillar changes the win rate. 50.45% is the Zerg win rate on maps with a pillar. If having a pillar indeed affects win rate, we should see a significant difference. Further, the use of global Zerg win rate is not suitable, because the mean is derived from the sample per se. When analysing match-up specific effects, we pivoted to using the match-up specific pillar win rate as the basis, 51.77% (ZvP) and 49.35% (ZvT).
Using two-sided t-tests, the results showed that the presence of a scouting pillar does not affect the win rate (p = .214). To unpack the effect of a scouting pillar in each match-up, we repeated the process with only the ZvP games and only the ZvT games. The presence of a scouting pillar has no effect on ZvT (p = .526). However, the difference in win rate between maps with pillars and those without pillars for ZvP is marginally significant (p = .073, d = .334). Zerg has a win rate of 51.99% win rate on maps with pillars, but that drops to 51.28% on maps without pillars.
The results suggest the effect of a scouting pillar on match outcome is more complex than one might assume. The presence of scouting pillars does not have an unwavering effect across all games, as it affects ZvP but not ZvT. I am sure some would be quick to point out that the difference of 0.7 percentage points in ZvP is negligible. However, it is important to highlight that the maximum difference in win rate between the best and the worst Zerg maps is just 4.5 percentage points. We should not underestimate the significance of the difference in win rate for the presence of pillars in maps.
Clearly, the results do not allow us to infer the exact reasoning behind the discrepancy across the match-ups. One plausible explanation is the relative value of scouting in the early game. The results imply that the information gathered via the Overlord on the scouting pillar has greater implications on Zerg’s decision making in ZvP than in ZvT. This suggests two plausible reasoning. One is that Zerg rely more on other ways of scouting in ZvT than in ZvP. Zerg would want to see the add-ons on the production buildings and selective tech buildings (e.g., Armory), as that helps to deduce the builds tremendously. The information is better gathered with Overlords going into Terran’s base from the side. The other plausible reasoning is that, compared to ZvP, ZvT requires Zerg to make less dedicated adjustments in the early game.
The effect of the scouting pillar might also be indirect. Players may pick certain builds on maps without the pillar. That is, the outcome could be due to the choice of builds and not the actual availability of scouting information itself.
Does metagame influence the effect of scouting pillars on outcome? And how? Most people would intuitively say yes, but I doubt anyone can back up their arguments with empirical evidence. We thought of using patches as a proxy for metagame in the analyses. Ideally, the results would inform us that the effect of scouting pillars is stronger in some patches (or periods) than in others. We could then, based on this information, deduce more precisely how scouting pillars affect ZvP. However, the limitation of the data makes it difficult to make comparisons across patches, because there are patches that have one map with no pillar. The problem goes beyond just sample size, as the comparison would then be map specific instead of patch specific. Thus, we did not conduct patch specific analyses.
This article is published at the best and worst time. Blizzard did not rotate the map pool for the latest season, and it is unclear if new maps will be introduced next season. Mapmakers’ interest in creating new StarCraft II maps is probably at its new low, so map improvement related discussion is rather meaningless. Conversely, this also implies that the current understanding of map design in StarCraft II has reached its peak, because the ladder maps are unlikely to be replaced by better maps. This would suggest that we have been making assumptions about the impact of certain map features that may be overly simplified or not hold. The use of machine learning could potentially lead to better and more interesting maps.
While our work shows some unexpected results, it is not without limitation. First, the difference in sample size for maps with pillars versus without pillars is obviously an issue for statistical inference. Second, the sample games from Sc2ReplayStats have selection bias. We could not access games that were not uploaded to the website, and there could be unexplained factors that contribute to the likelihood of uploading replays. For example, those who upload replays may be more serious about improvement than those who do not, and this could potentially affect map veto decisions and the choice of games to upload. Third, which is related to the second, the selected games were played by “average” players on ladder. It is unclear if the findings are generalisable to the pro level. We initially wanted to sample games from GSL, because it covers every patch. But the number of games for maps without pillars is simply too low.
Special thanks to those on r/allthingsterran who helped to code the maps. Also, big thanks to Henry for the huge Patreon support!
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