Officer Greg put together this explanation of how stratification can help your generator feel more random than random.
Humans tend to be poor estimators of randomness. […]
This is a problem for procedural generation. If your map consists of the same tile used over and over again, players (and designers) are likely to think that the algorithm is bugged. In a different strain, a map that has all the interesting features in one corner not only looks bad, but also makes for a fairly uninteresting play space. Small sample sizes selected without replacement just don’t cut it for procedural generation (and large samples are often not feasible.)
A solution is stratification. Stratification involves dividing the sampled distribution into segments (i.e. strata) and sampling randomly from each one.
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