Not sure if it's purposeful bit masking/shifting or their PRNG is really really awful, but by making small changes in the seed you can adjust the layout of the map.
Some examples: 1-340 all seem to be the same, with different patches 341 has the same geography, but trees instead of desert 342 changes the geography.
The bit twiddling behind this is unclear. 341 to 342 just changes the right most two bits. If you find anything interesting, please post. Anything to reduce spending time in preview :)
Here's the string I'm using which has the various settings, in case that's relevant:
eNp1Ur1LQlEUPyc1zSAahAjCHFwNsoaG8N6CiIj6G/LjCYL65 KlDNeTgWLS01JJri1tDmxT0AQVSU5vR0lBhFLUEdu577z6frzpwf u93z/e59yEg9IMbSCocgDOfO6nGswANLtWfVAsFRYuommI3DyS1c kqJqJneYCWv5NYjiXiRgisMdKkwX0ZT884KnmJJzfdaSpqiFI1EQ wfLWjyfKeecuYAqkr8a1LWzBaFORyixFnUUClghoEiySfEks5l0G iA0RzovGiDiZqC++LCxx9CImeAmaZuWRkJaliRZ5f+6wpJM2+pM6 fJuI0bTErUwo3y8SwxnVTgRd16Oa1/nzRh+H73driTWGE4uBF7b0 XqMnF6xZ58FB/tCTuQqIGu2mOm6Z3hzLeSZoUdkBATwGYLGsgtwe IhYbZsgNAZytJgsE+CY1uVTbvIoyR1z7kEXMSuKBwVcCtAbWpOhQ fkuRz4uvaPdEMqPgn2GVHfDK9n2zNbfMcjvh7Dv4bCE+R/P4BcNU xY8uaxp6D6bXnnihxxdgoioD7IZJ/3nM0sZ32GuX7cLutJmMBI5v fgB8sOilg==<<<
Some further info here -- https://wiki.factorio.com/Map_exchange_string_format
Not sure what exactly it is you are looking for. For up and coming runners we usually recommend to stick with one of the existing categories and use a map from the leaderboard, that approach doesn't require any time in preview ;)
Regarding the map exchange stirng you posted: Why is there so much water? Why are cliffs and uranium enabled?
This month's speedrunning update can be found on Reddit here:
