They wanted the judges to be able to make court decisions without regarding politics.
The Encomienda system left a lasting impact on the newly independent Latin American nations. Much of the local belief system and structure was destroyed and replaced with Catholicism. Many of the natives had been treated so poorly, abused, and taken advantage of that repairing the broken relationships was near impossible. The natives were extremely fearful of the Spanish and those that replaced them in power. They had been seen as less than human and simply a work force to use until they died, much as some slaves were seen in America decades later. Natives would face severe discrimination for years after.
I would say a city on a river port to an ocean and/or lake. You have access to water and a harbor that you could receive and export. If the river runs through the city, the transportation of goods etcetera would be easier. That could also give you recreational activities like water sports and boat rides.
<em>I hope this helps!!!</em>