This is something Civ IV has needed for some time. The simple fact is that most of the food we eat comes is farmed, not wild. Early civilisations would have needed to discover wild maize, rice or wheat before they could commence planting elsewhere. Thereafter, though, organised agriculture is one of the factors that enabled city dwelling, as we know it. Crops are planted where fertile land exists from which food can realistically be transported to the population it sustains. This
may, in fact, not be the specific locations where it grows wild. This mod addresses that.
The same could be applied to animal domestication, too. For example, the horses that our scouts discover on the map are actually
brumbies. Brumbies need to be found before a civilisation can commence breeding domesticated horses. However, in reality, captured brumbies could be relocated for stud breeding. Placing pastures only where brumbies grazed prior to human settlement is just plain unrealistic. With sufficient time spent on breeding programmes for domesticated horses, new studs could be established across your civilisation. This is how farming works. However, at any given time, it would mean making a
choice between domesticating, breeding or utilising as beasts of burden. There are trade-offs with each. The same could be applied to other land animals.
I'm keen to peruse some of the code in this mod to see ways this could be applied. There are other problems with food supply in Civ IV which (on the face of it) seem more complicated than the issue this mod addresses. Principally, that after the development of pickling and other preservation methods, food was able to travel greater distances. The result is that food is generally grown in rural areas, away from cities. Thus, farms/pastures outside a "fat cross" should be able to supply food to cities to which they are connected by road (after discovering "Preserving"). The same applies to fisheries. Similarly, food should be transferable between cities post-preservation also. This would fix the anomaly whereby cities with fat-crosses full of farms have improbably large populations (Real rural service-towns are often quite small) but cities surrounded by population/labour intensive mines, quarries and villages/towns can't get to the size required to service them (and some buildings are natural job creators like Universities, Banks, Corporate offices, Ironworks, etc). In reality, food is grown in sparsely populated plains/grasslands, but people live in higher concentration where there are jobs (that is, labour intensive industries, bureaucracies, commerce etc). This mod doesn't fix that anomaly, but that is a more complicated challenge for another day.
The problems with the way Civ IV handles food and population distribution are many, and each involves different fixes. The problems are such that they
can be fixed individually. This mod fixes one of them quite well. It's code will also be very useful for fixing some of the others in the future. The first challenge is usually the hardest, and you seem to have cracked it. So,
thank you and
well done.
I hope this mod becomes the catalyst for further incremental improvements.
...) because I really the germination of this idea, pun intended 
.
to build, like Workers/Settlers. That unit will destroy itself to create one crop or herd that you already have access to on a suitable square. Then issues of game balance can be addressed simply by tweaking the amount of 
the unit costs.
