The other thing that bugs me is that starting bias is near ivory. Of course. Siam is an Elephant (and also gunpowder) empire. but cities are founded by rivers, big or small. Elephants are always caught from the deep jungles, several times elephant catching party went as far as what's now Surin province. or alternatively as a tribute given by vassals that have these. (and sometimes with handlers handed over to Bangkok)
don't forget the fact that 'Bang' is built alongside waterways of any type. (unless the ingame buildings actually extended the said 'watereways' after a construction or even a Bang can build right next to each other, ultimately recreating Venice of the East.
Elephant catching process (and handling post process) is so much an art, and sorcery. involving the use of magic, this is due to the fact elephants are imposingly big, and can be fierce. an elephant died in military serviec earned the same cremation honor as human nobles.
The best known catchers, and handlers were Suai people. they got the name because they catch elephants and handed over to Kings (paying 'Suai'), these men were often recruited by the central government specially to handle these beasts. These were related to Khmers of the antiquity.