Wow, this map is progressing nicely. To answer your question, Clercon, based on what I have seen of Venice and other Italian cities (such as this google map of the core of old Florence http://maps.google.com/maps?f=q&sour...26758&t=h&z=16) your streets seem "about right". That being said, I would put a wider east-west thoroughfare either on one or both of the banks of the canal, or running parallel to it on one side or the other. Given how much traffic would be flowing from one end of the city to the other (granted, much of that by canal), such a road would be likely to exist.