I often find it difficult to agree with other peoples footprint calculations. To me, the embodied energy of a commodity is nearly impossible to accurately calculate because many different infrastructures are so tighlty linked together, it gets difficult to divide and sort. I mean sure a tomato is shipped into the city in bulk, but the distribution doesn't end there because it still arrives locally on smaller runs which involves a lot of trips by a lot of trucks. It isn't like a train is backing up to your local foodmart and unloading tons of food. Not to mention, these large trucks and distribution centers are often refrigerated which ups their energy consumption plenty. Regarding specialization, sure some things grow better in some places, but we often end up with a homogenous product that way. There are literally thousands of tomato varietals, but how many end up in the market? Industrial farming is anti-diversity. And we end up with places like Almeria, Spain: Costa del Polythene.