So asks Sam Wilson on Twitter. You can parse this question a few different ways, but I take it to be about location theory and, indirectly, topology. That is, why are there so few cities with multiple water connections between different independent nodes?
First we might check the historical premise. Stockholm used to be called “Venice of the North,” a variety of Dutch cities are based on canals, check out the (now largely defunct) Marsh Arabs from southern Iraq, plus a variety of arrangements in southeast Asia over the centuries, such as kelong, or the Pang uk of Hong Kong. There is a long history of stilt houses on water, including but not restricted to Chiloe, Chile and Nipa huts in the Philippines, some of which are designed for wet areas.
But I digress.
In any case, many cities seem to have a much smaller number of nodes connecting to the water. Check out Duluth, Minnesota. There is a dominant port, with most local connections to that port running overland rather than by water. And if a goods shipment is headed into Duluth, you pretty much know where it will arrive. The same is true for Rotterdam, as no one is angling to reach those inner, smaller canals of Dordrecht with their bananas.
The greater the anonymity of exchange, and the greater the distance involved, the stronger is the role of a formal port as a centralized supplier of trust and also buyer-seller coordination. That will imply a small number of water nodes, all the more so as globalization and specialization proceed.
But if you are a Marsh Arab wishing to trade some rice for some coriander with your neighbor, and the next day lend a sowing needle in return for some gossip, to a different neighbor, such idiosyncratic bilateral yet multiple exchange nodes and networks may work pretty well. You can think of multiple node cities as doing a great deal to enable non-regular, non-standardized barter, but that becomes less valuable with economic growth.
A related approach is to ask when it is more efficient to settle nearly contiguous islands, as opposed to dry land next to water. In earlier times non-monopolized access to fish, trade, and water transport were main reasons, plus Malthusian conditions elsewhere, such as in the resource-sparse, low-yield Veneto. Venice was settled long before a mix of accident and leadership skill led to it becoming a primary conduit between East and West and thus a wealthy and powerful commercial republic.
For a variety of propositions about monetary economics, there are corresponding propositions about topology and location theory, the trick is to see them.