If we connect our 15

capital to a new 5

city using 5 tiles of roads, we have the following effects:
- -5
/turn cost (-50% with the Guilds commerce policy).
- +5
/turn income.
- +1
with Representation liberty policy.
- +25%
with Railroads tech.
- Double weight for citystate yield distribution.
- Units can move much faster, especially through rough terrain.
Since I often want to channel citystate food or culture into a newly-founded city, connecting the city for the higher yield weight is very helpful. This is the basic

income from connecting a trade route:
Another way to read this table is what #roads we can connect a city without losing gold. Harbors cost 3

/turn so if our capital is at least size 8, the maintenance cost is
always paid for by the trade income.