The number of provinces a noble controls determines his status or rank:
provinces rank --------- ---- 1-3 lord 4-7 knight 8-11 baron 12-15 count 16-19 earl 20-22 marquess 23+ duke
In addition, if a character has control over every province in a region, and the region contains at least 15 provinces, then the character is given the rank of king.
Provinces may be directly owned, if the noble is the owner of a castle, or indirectly, through other pledged nobles.