The next Economic Policy to enhance adjacency bonuses for a district, this time the Commercial Hub. Like the Harbor, its adjacency bonuses yield Gold, but land-heavy maps make it easier to get good bonuses for the Commercial Hub - it's rare to have more than 2 Sea resources in a suitable location to get a bonus of +2 or more for the Harbor, whereas every tile next to a River will yield a +2 bonus for the Commercial Hub, which can easily be increased to +3 or more if other districts are adjacent to it. That means that most of the time, it is more profitable to use Town Charters than Naval Infrastructure. The latter one, however, is available earlier, and there are other possibilities to enhance your Gold input anyway - you should always think of which one exactly will yield best results for your particular empire.
Civilopedia entry Edit
Traditionally, the granting of a town charter gave it and its inhabitants the right to certain privileges in the feudal system. Townspeople were burghers, as opposed to serfs, and “free” in the sense that they were protected by (and owed allegiance only to) the king rather than the local manor lord. Charters also gave the burghers some semblance of self-government, in that the rich merchants would be allowed to choose a mayor and hold a market or faire under their own auspices … so long as acceptable to the king, of course. As early as the 10th Century AD, German towns were being granted town charters, with their own militia, courts, and taxes … the model for all those after.