Food deserts to me are an important 'issue in urban economics' that I thought connected nicely to the idea of community gardens. A food desert is a low-income residential area with little or no access to supermarkets or fresh food. Often, when a community garden is built, vegetables and herbs are planted so that residents can have access to affordable fresh foods. So they're useful and pretty!
Here's a recent CNN article with a link to a new, interactive 'food desert locator', and here's some more info on how some local organizations in Detroit are creating small urban farms to remedy this situation.