Ok, so on to the start of the islands. The outer eight are the islands directly towards the outside of the city, obviously. These islands are the first ones foot traffic passes through on the way into the city. These have changed drastically in the last few centuries, as adventuring was outlawed in the city proper. The outlawing itself was passed unanimously through the senate once they realized that anyone dressed as an old man in the darkest corner of the tavern could sic a group of adventurers on anybody in power just by saying they were “up to something.” At any rate, adventurers are now restricted to the outer twelve islands.
The outermost eight are the the point of entry to the city, where the guards are trained to distinguish adventurers and normal visitors. “Normal” people are given passes, which allows the bearer to travel through the outer eight, or pay to get on a barge to the island of their choice. Adventurers on the other hand are required to stay on the outer eight. These islands are not represented in the senate, and the names they once had have mostly been forgotten.
These islands are populated almost entirely by seedy taverns and inns, with very few personal homes. What personal homes there are are owned by eccentric retired adventurers, and are some of the weirdest places in the city. Bar fights are common, and guards are instructed to allow fights to play out, and arrest those who are unconscious. This means the area can be very dangerous at night, and that prices are relatively high, to recoup losses from collateral damage.
The inner three of the “four” are markets specifically geared towards adventurers. This means blacksmiths, scrolls, potions and magic-marts. There is an entry fee of 5 gold, which was the compromise down from the .5% tax that it was previously. This, and the 500 gold pass to enter one of the other islands is the major ways the city pays for civic improvements. The market districts are also the place where a majority of the money in the city is made (note that I didn’t say this is where the commerce occurs), since the merchants who work here gouge the hell out of the adventurers (buying something and then selling it for twice as much as they bought it for).
The final island in the twelve is sort of an anomaly, since it used to be one of the wizard college islands, specifically necromancy. This was until about fifty years ago, when a group of drunken students from the conjuration college decided it would be fun to start talking about the “loads” of liches and vampires and mummies and the like at the college while bar crawling on the outer eight. This lead to a herd of adventurers realizing that they were needed to cleanse the city of these horrible undead monsters. The fact that there were many of these things at the college doesn’t aid their argument, since these individuals were considered to be upstanding members of society. At any rate, the adventurers pulled down the college and destroyed the general life on the island (mostly because it was “creepy”). The city considered this to be very unfortunate, but there wasn’t a lot they could do to fix it. No more necromancers wanted to set up a college in the city proper and risk the same fate, and nobody sane and alive wanted to live there anymore. This lead to the island being abandoned by all but the wandering mindless undead. Since this seemed more or less right up adventurers alley, the city allows them to wander this island as they like.
This more or less describes the general information on the adventurer focused islands, and pretty well wraps up the way the city economy works.