It seems that it will provide 1 extra amenity of luxury resources for EACH kind of luxury resoures which improved inside the city boundary. It means that if you have 3 spices, the Great Bazzar provides only 1, but if you have 1 spice and 1 citrus, it will provide 2. But I really got confused about how it works about Strategy resources. I got a city A with 1 Uranium mine, 1 Niter mine and 1 Coal mine. No other Uranium in other cities. I got +6 Uranium per turn, so I assumed the Great Bazzar provides 3 extra Uranium for city A have 3 kinds of Strategy resources being improved. In another city B, there was 1 Iron mine and 1 Coal mine. I got +4 Iron per turn, due to the assumption above. But then I got a City C, there was 1 Horse pasture, and 1 Niter under an encampment. I got +8 Niter per turn. I think there is a +5 for City A, so it's a +3 for City C. Maybe only the Horse pasture is regarded as "improved Strategy resources", so only +1 for the Niter? In fact City C also had a Offshore Oil Rig 4 tiles away from the city center, maybe it didn't count, too. But I assumed I will have +4 Oil per turn for the Horse Pasture. I had abundant oil inside my border so a bit difficult to confirm. To sum up my assumption: If X(2 or above) kinds of Strategy resources are improved with the corresponding improvement inside the city border of radius 3. Extra X strategy resources will be provided for each kind. If a stratery resource is improved by a distric or beyond the city radius of 3, it will not count into X. But Extra X(1 or above) of this resource will still be provided. I hope anyone can help to confirm my assumption. Maybe @Victoria know more about this?