I thought i would go through an economical progression to give people an example of the sort of advancement which occurs ingame:
Here is the progression of 'marble' to 'marble statues', a relatively 'short' line of advancement but can still take quite along time if you dont have access to the correct technologies and buildings.
1) in 1066 we discover marble is present throughout our lands in modena.
2) as we can see on the province view, marble is now accessible to all within modena. And the temple and castle holdings can now construct quarries to harvest the marble.
3) so as we have access to marble, we can construct mines to harvest said marble, but we first must have a 'serfs hamlet' in our barony. Which represents the workforce required for us to remove stone from the ground.
The serfs hamlet is one of the renamed buildings from the castle settlement building line, it is not a brand new and seperate building.
4) with our marble quarry constructed, the barony of modena receives a tax boost. The quarrying of marble from the ground has now opened up more buildings option within the nearby barony of Carpi. And as such we recieve an event informing us that artisans must be encouraged to the province. (the localisation is a little loose atm but will be refined before we release the mod).
5) the above event is what unlocks the additional sculptor related buildings within the city of Carpi. After a long while of improving the infrastructure of the City (through both the mayor and countess of the province) the construction of a Marble Workshop in the city will see the production of statues increase greatly.
6) With the construction of a marble workshop, the province has established itself as a producer of marble statues, increasing the wealth the province receives by a large amount. An event fires informing us of this.
7) The new province modifier of 'marble statues' replaces that of just 'marble' and is for all to see that the province is a producer of fine statues.
Obviosuly the marble still remains in the province and further upgrades to the quarry building line can be made, as to further increase the provinces revenue from marble..
The above is just one example of many resource related improvements related to provinces with the access to the required resources. i.e. marble leads to statues, iron leads to forged iron, cattle leads to leather and can lead to beef meat etc etc.