The simplest supply chain is a straight line. Corn is grown in the yellow areas on the first map, and darker colors indicate higher production levels. That corn is transported to hog facilities at the endpoints of the lines in the second map. The third map shows hog production by county, with darker colors representing more hogs, and the lines lead to hog processing facilities.

In reality, corn is fed to hogs directly - as in the first example - and indirectly as Distiller's Dried Grains with Solubles (DDGS), a co-product of ethanol production. The top three maps here are the same as the first set, but below them we see corn production flowing to ethanol plants where it is used to produce ethanol and DDGS. The DDGS flows to hogs and - as before - hogs are transported to hog processing facilities.

We can also add other crops. In this case, soybeans are not fed directly to hogs but are first transported to soy crushers to be processed into oil and soymeal. Soy oil, like ethanol, is a co-product considered separately, while soymeal is fed to hogs.

One of the main reasons we are interested in tracking these flows through the supply chain is so that we can calculate environmental impacts at each stage and connect them to the final product. In this example, we return to the simplest supply chain, and show greenhouse gas emissions from corn production, from hog facilities, and from hog processing, as well as the emissions from transporting goods along the supply chain. While a processor may only be able to directly measure the emissions from their own facilities, the FoodS³ model provides a way to estimate the total emissions embedded in the final product.