How had the knowledge of land west of the Mississippi River changed since the early 1800s and what impact did this have on settlement patterns?

How had the knowledge of land west of the Mississippi River changed since the early 1800s and what impact did this have on settlement patterns? In the light of these changes, how would the population be expected to expand in the next few decades and what impact would this have on the balance between slave and free states in the Senate?
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