[Taqwus]

Astral Window gives you population estimates. Useful to know where to send Black Deaths, Volcanic Eruptions, Tidal Waves and Harvesters if you're the sort of evil chap who's inclined to do that.

Haven't tried both Harvester and BVC -- my usual BVC holders have been cheap Black Servants, when I'm not sadistically "gifting" them to an AI through messages.