I've been thinking a bit about economics in the Imperium as I continue to work on Tarvenhive. In particular I've been thinking about the upper end of the wealth distribution, since that is where the power will tend to lie.
One has to start somewhere, so the sensible place to start seemed to be with the developed world today, since I suspect that a hive city should be at least equivalent to the present day developed world in terms of technology, manufacturing and overall wealth. Now, I've set the population of Tarvenhive as a little under a billion, whereas the present population of Europe is 730 million and that of North America is 520 million, so Tarvenhive is either roughly one and a half Europes or 2 North Americas in terms of population (and as a first estimate in terms of economy too). Using the whole of Europe or North America, rather than just say the EU or the United States also seems helpful because that way, for Europe we include places like Russia, Belarus and Ukraine as well as France and the UK, and for North America we include places like Mexico, Cuba and Guatemala as well as the USA and Canada. This seems like a good idea since although on average I expect a hive city is equivalent to somewhere like the UK or the US I also suspect that it would probably have rather greater income inequality.
In terms of totals Europe has a GDP of $20 trillion while North America has a GDP of $17 trillion, so overall I would expect Tarvenhive to have a GDP of something like $30-40 trillion at least. So much for totals, I don't know about other people, but for me once money gets that insane it starts to loose meaning. Slightly more useful I think is to think about the wealth, and comparative size, of the upper classes, since their wealth, although still vast, is somewhat more comprehensible.
A useful bottom level to 'the rich' is someone with a net worth of more than $1 million, which is used by a lot of other organisations as well. In Europe there are about 3.2 million people in this band (0.4% of the population), while in North America there are slightly more, about 3.35 million (0.6%), so if I want Tarvenhive to be a bit more unequal, more like North America, then Tarvenhive would probably have at least 7 million people who are the equivalent of US dollar millionnaires in 2011 money, maybe as many as 10 million (1% of the Hive). Rather nicely this is similar to the population I had envisaged for the Upper Hive. Above this there is a convenient definition of 'ultra-high net worth individuals' as those with a net worth above $30 million that roughly picks out the '1% of the 1%' as it were, the top 1% of those with a net worth above $1 million. So Tarvenhive would have something like 70-100 thousand such people, which is rather a lot of extremely wealthy people.
Finally then how rich is the richest person in Tarvenhive? Well the richest person in Europe is Bernard Arnault with $41 billion, while the richest person in North America is Carlos Slim with $69 billion. So the richest person in Tarvenhive probably has the equivalent of at least $80 billion, probably more. In particular once you start getting up to this level things get more complicated because the richest person in Tarvenhive won't just have interests in Tarvenhive, they will have holdings in other parts of Tian as well, and possibly even off world.
If you start thinking about the fact that Tian as whole probably has 100 times the population of Tarvenhive (maybe even more), then a person with a net worth of $80 billion isn't exceptional. If you go down to number 100 on the list of the worlds wealthiest people they have about $9 billion dollars, so if the ratio between the richest person on Tian and the richest person in Tarvenhive is similar, the richest person on Tian might well be pushing towards being a trillionnaire, especially since they will definitely have assets offworld as well as on Tian itself. That would be larger than the GDP of a country like the Netherlands or Indonesia!