The location of a garden is key to its success. If a garden is never visited or tended to, then the success of that garden is unlikely. However if a garden is located where it is visited regularly, then all things being equal it will more likely be used and tended to. Using permaculture principles, things which need regular tending are closer to your house than those that do not. Thus seedlings need to be visited every day. However the main veggie garden could be visited every two or three days.
Available sunlight is an important factor when deciding where to place a garden. Vegetable food crops generally need at least 6 hours of sunshine. On small urban blocks micro-climates are a huge factor with buildings, fences, hard surfaces, and trees potentially having a significant impact within surprisingly small distances.
The lay of the land can also influence a garden location. Steeply sloped blocks often require retaining structures to prevent soil erosion.