Odds are, you are reading this from an urban area. Maybe not from one of the mega-cities ballooning in parts of South America and Asia, but at the moment over half of the world's population resides in urban areas. Although definitions of 'urban' vary geographically, we all agree it relates to population size and density, the public provision of infrastructure and services, and a reliance on non-agricultural income sources. Concentrated areas of human population have been touted as the model toward which we need to move in order to achieve more efficient lving and reduce humanity's ecological footprint. And in theory there is validity in this - compact living arrangements should decrease per capita energy consumption and physical space occupied, streamline waste disposal, and reduce emissions from private transportation (which is often unnecessary or impractical). However, as a nifty Science Magazine infographic has recently illustrated, cities retain more heat than rural areas with air temperatures 1-3°C higher, exhibit worse air quality (Beijing, anyone?), house more impermeable surface so groundwater can't recharge, and have this nasty tendency toward light and noise pollution (that honestly is bad for both people and the rest of the fauna we share the world with).
Now those are all difficult challenges. An article on the urbanization and food system connection pointed out that there are other implications of cities beyond their immediate footprint. The authors voice concern over the potential loss of fertile agricultural land due to development - particularly because many cities were originally embedded in these productive zones (like in delta regions). They also note that urbanites tend to eat more animal protein. And as you guys know, the environmental impact of meat is pretty high. Some of the less well-established links between urbanization and food systems relate to changes in social norms and attitudes - for instance, people may be less particular about their food's environmental impact when not in close proximity to where and how it's grown; days tend to be jam-packed in metropolises and so convenience and packaged foods are popular; or even on the retail end, the need to err on the side of overstocking shelves to suit all consumer preferences and needs may result in greater food spoilage and waste (and few places to compost it).
The article also notes that the impacts on the farmers themselves, especially smallholders in these newly and rapidly urbanizing countries, is very little studied. Yesterday also happened to be World Hunger Day, as we continue to strive toward the Millennium (and now Sustainable) Development Goal of ending world hunger. This connects us to food security concerns, which are often concentrated in rural areas - as being poorer and with access to more limited supply and variation in food. But it's also important to recognize that hunger is not just a rural versus urban divide, and that cities often have great income disparities leading to inequality in access to and quality of food among the urban poor. The industrial revolution's rise in malnutrition as former farmers flocked to cities for factory jobs was just the beginning, and this continues to be an active area of study in both developing and industrialized nations.