Jensen does little more than trace trade routes for you, so start with Hay's chapter on the Bonds of Trade. The beginning section introduces the useful distinctions between purely local commerce, regional commerce, and international trade. His comments about transportation ("Communications and Trade") are also useful.
A fleet or an individual ship made many more stops than the map implies, and went to more ultimate destinations. There is a limit, of course, to what can be shown on a single map, but it would be easy to be misled here.
One thing is evident, however, from the maps: these were coastal routes. One reason is that the more stops one made the opportunities there were for doing business, but this coastal sailing is also a reflection of the state of navigation at the time. It was simply too risky to sail out of sight of land for more than a day or so.
The great north-south axis was along the Rhine River, across the Alps and down to the Italian ports. Further west, the Rhone River carried goods, though rather less efficiently. Eastern Europe has no good north-south routes until one is well into Russia.
The one good east-west route runs from Poland through northern Germany and into the Low Countries. A second route follows the Danube River, tying the Balkans to central Europe.