It is located in CIV4EuropeInfo.xml file in GameInfo. Here is the EUROPE_EAST define:
Code:
<EuropeInfo>
<Type>EUROPE_EAST</Type>
<Description>TXT_KEY_EUROPE_EAST</Description>
<Direction>east</Direction>
<bStart>1</bStart>
[B]<iTripLength>2</iTripLength>[/B]
<iMinLandDistance>4</iMinLandDistance>
<iWidthPercent>20</iWidthPercent>
</EuropeInfo>
I would say bStart means that this is where you are allowed to start the game in and iMinLandDistance defines the minimum distance between land and Europe plots. Not sure what iTripLength and iWidthPercent do, but they probably define the shape of the Europe plots.