Pohjanmaa - or how do you call it?

I was reading a Blue1 Dream magazine where there was the attached story about a costume from my neighbourhood, Pohjanmaa.
The problem is how to translate it to english.. Direct translation would be bottom-land. Many people call the area like in the article, as east botnia, or even use the swedish word österbotten (as it was any easier to get), both meaning "east bottom". This refers to the time when Finland was part Sweden, and Pohjanmaa was the old sea bottom on eastern side of the bay. This is a similar type of geocraphical relict as East Indian Islands in Caribian.
I often use the phrase west coast, which might be more easy to comprehend without the knowledge about the finnish history.