Hi Robertus Satherbus,
Traders that walk around a map like Lugdunum will, of course, take more time than those that only visit a warehouse or two near the "road to Rome". Whether that affects the volume of trade depends on how much trade you are trying to do with that city. Since cities have an annual limit to the amount of each good that they'll buy or sell, the length of a trader's journey may not matter even with trade in certain goods maximized.
If it is important to sell a lot (say 70 carts/year) of expensive goods to one city, then it may be wise to make sure that traders never travel far from the path between the entry and exit points. However, if a small amount (say 24 carts/year) of exports is sufficient, then it won't hurt for traders to wander around. The volume of imports is usually not a critical factor, but if it is then the same logic applies.
When I designed Lugdunum, I didn't have much feel for these things. Just to be safe, I decided that traders could go a short distance into the large open area, but no farther than that from the "road to Rome". That decision caused a chain of others. With the warehouse for oil in that area, all houses that needed oil (large insulae or better) would be there too. While furniture could be moved around the map, it seemed to make sense to build a few grand insulaes in that area (fed by the "farming island") and make almost all of the remaining houses small insuales, which would give the required Prosperity (and minimize the amount of imports). Those small insulaes would need pottery warehouses scattered around the map, and to prevent traders from going to one, I decided to not export pottery (which was fine, since Lugdunum can make plenty of money without selling pottery, even ignoring the lucrative native trade).
The above is just an example of one aspect of city design. Other ways of building Lugdunum are fine--in fact, I'd probably do things quite differently if I built it again.
[This message has been edited by Brugle (edited 06-27-2000).]