For each destination, between four and seven routes were created
on different modes. Each route runs between the centroid
of Iowa and the weighted centroid of the destination region.
The road routes mostly run on Interstate Highways with a small
amount of US and State Highways. The rail routes are organized
by Class I carrier. Where possible, track owned by the carrier
was used, otherwise where they had trackage rights. Only
a few destinations have plausible water routes.
In many cases, Chicago (for road and rail) and St. Louis (for
water) are used as hubs. For instance, to get to the Northeast
US centroid from Iowa, all valid routes enter through Chicago.
Therefore, the routes to the Northeast are a combination of
routes from Iowa–Chicago and then Chicago–Northeast US.