Just encountered a wonderful spawn of 8 geysers on a single, mountainous/valley-ish map, 300x300. Which I must say, I'm pretty happy about, especially with 4 of them being in the mountain, lets me keep my colonists alive a bit more.
However, I did notice that I did not have a single patch of rich soil on the entire map, so it has that going for it, means I'll need to work harder for those potatoes.
http://i.imgur.com/M1t6RM0.png
Has Geyser generation been edited for Alpha 4? I do not recall receiving as much in prior builds. (About 4 to 5)
I don't know if the terrain has changed or if it's just luck, but I also just got a map with 3 overworld steam geysers fairly close to one another.
The number of anything should be proportional to the size of the map, so if you have a huge map you'll get more geysers.