A growing body of research suggests that the suburbanization of food retailers in North America and the United Kingdom in recent decades has contributed to the emergence of urban 'food deserts', that is, socially-distressed neighbourhoods with relatively low average household incomes and poor access to healthy food . While more and more large-format supermarkets are erected on suburban lands, smaller grocers in older central-city neighbourhoods seem to be rapidly disappearing, leaving potential food deserts in their wake. This paper explores the historical and geographical evolution of supermarket access in a mid-sized Canadian city: London, Ontario, 1961–2005.
Why examine access to supermarkets? A healthy diet can reduce the risk of many chronic diseases . The majority of these health problems can be linked to a diet with low fruit and vegetable consumption [3, 4] and eating large amounts of sugary or high fat foods . National surveys indicate that most Canadians shop for food at a local supermarket, where the widest variety of products can be found at the most competitive prices . While supermarkets also carry unhealthy foods (e.g., chips, soft drinks, and processed foods), these items are more readily available at neighbourhood convenience stores, which are less likely to offer items supportive of a healthy diet. What happens to residents when the only supermarket in a neighbourhood closes? For certain disadvantaged populations who do not have access to a private vehicle, residing in a food desert may have detrimental effects on overall health and quality of life [7, 8].
Environmental inequity occurs when a locality has disproportionately many undesirable characteristics and few desirable characteristics . While environmental equity research is almost always focused on the 'undesirables', that is, identifying demographic disparities in exposure to environmental hazards such as air pollution, toxic waste and other LULUs (locally unwanted land uses), our concern in this paper is the equitable distribution of a particularly 'desirable' sub-category of land use which offers easy access to an array of food and household items at competitive prices: the retail supermarket.
Our primary objective in this paper is to use network-based GIS accessibility measures to determine the extent to which food deserts exist in London. In order to meet this objective, the paper will provide answers to three fundamental research questions.
1. Do systematic spatial inequalities in access to supermarkets exist?
2. Have spatial inequalities in access to supermarkets increased or decreased over time?
3. Do systematic socioeconomic inequalities in access to supermarkets exist?
The scholarly contribution of this paper is twofold: first, for spatial equity research, it offers network-based GIS methods which consider two low-cost travel modes (walking and public transit) for determining accessibility; and second, it gives critical contemporary and historical insights into an urban health issue of increasing present-day interest: the accessibility of healthy and affordable food for disadvantaged populations.
Urban Development, Grocery Retailing Trends and Access to Healthy Food
Grocery retailing practices in North American cities have undergone many changes over the past century which have largely been driven by prevailing patterns of urban development . The introduction of the automobile has perhaps had the largest impact on shaping cities over the last century, allowing people to move about much further and more freely, fuelling the rapid postwar suburbanization of the population and the deliverers of the goods and services which they consume . Investment in highway infrastructure, particularly in the period immediately following WWII, cemented the dominance of the automobile as the preferred mode of transit. This form of privatized mobility, however, was not democratically distributed; only those with sufficient wealth could afford the luxury of auto-mobility .
The automobile provided the opportunity for many residents to move to the suburbs, but it was a cultural ideal that stimulated the move to the suburbs from the inner-city. North American society views cities as unhealthy places to live , with poor sanitary conditions, high pollution, unsafe and cramped living spaces. The suburbs were seen as the binary opposite providing healthier opportunities for its inhabitants . At first, retailers and offices remained in the city while residents moved to the suburbs; however, by the 1970's many businesses and retailers (including grocery stores) were moving closer to their predominately suburban customer base .
Food retailing, like most other forms of retailing has seen an increase in both store size and the implementation of chains. In the mid 19th century food was typically obtained through small independently owned markets which were an integral part of residential neighbourhoods. By the turn of the 20th century food retailers had begun to organize into chains, most notably the 'The Great Atlantic and Pacific Tea Company' (A&P). Chaining allowed retailers to lower operating costs, increase profits  and use sophisticated location analysis to provide the most rational spatial arrangement of stores for maximal profits . These resources were not available to independent food stores as they could not afford the associated costs. Chaining was followed by the formation of supermarkets in the 1930's, which had a larger selling area and offered a greater selection of goods . Thus, with stores growing larger in size and investment in location analysis, it was inevitable that the overall number of grocery stores per capita would decrease, and retailers would likely follow their wealthier customers to the suburbs.
Most recent to emerge in the urban food retailing landscape is the giant grocery 'superstore', which can be defined as: a single level store with at least 25 000 square feet of sales area, which sells an array of different foods and household items, and includes a very large parking lot . The establishment of giant superstores on suburban lands meets the physical needs for store development as there is more land available for parking, it is easier for trucks to load and unload, these lands are usually more accessible to highways, and they allow for the development of much larger stores . While superstores are often cheaper to construct in suburban neighbourhoods, they still have created new challenges for planners and engineers around traffic, parking, noise attenuation, public transit and other related issues .
The relocation of supermarkets has been associated with urban development and the physical need for more space, but economic interests were of course the driving force and the fact that major chain stores, from research and experience, typically know where to locate to maximize profit. The location of supermarkets has always been within close proximity to customers with money , while older neighbourhoods have filtered to lower socioeconomic status, the suburbs have typically become more affluent areas; as wealthy residents left the city in favour of suburban living, the supermarkets followed . The effect of the economies of scale parallels the movement of much larger stores as they allow operations to become more efficient . Superstores were able to increase profit as they had lower operating costs, a greater product range, and larger catchment-areas, creating spatial monopolies within their region . Larger stores also meet the social needs of its residents; they have the shelf space to carry many multicultural food items demanded by today's postmodern society and allow for 'one-stop' shopping, as people can find numerous household items along with groceries under one roof, saving valuable time .
The rise of the suburban superstore and abandonment of smaller inner-city supermarkets has also presented challenges for planners and public health policy-makers due to the uneven distribution of healthy, affordable food opportunities [7, 18–24]. Several U.S. studies have discovered food deserts in older urban neighbourhoods of low income and high Hispanic or African-American populations [25–27]. On the other hand, recent studies of Canadian cities suggest that urban food deserts are not a problem in Canada. A study of the city of Edmonton, Alberta, found that low-income neighbourhoods near the city centre actually had the best supermarket access . Furthermore, a recent article in the International Journal of Health Geographics by Apparicio and colleagues found that food deserts are "missing" in Montreal and access to healthy food is not a major issue for low income urban residents . Meanwhile, results of studies of food access in the United Kingdom are mixed, suggesting that no clear relationship exists between supermarket access and variables such as location, income, or race in the cities of the U.K. [23, 30, 31].
The current literature is inconclusive as to whether easier access to healthy/unhealthy foods influences one's overall diet; however, it is widely acknowledged that a healthy diet can reduce the risk of many chronic diseases, including type 2 diabetes, heart disease and certain types of cancer . The majority of these health issues are associated with a diet low in fruit and vegetable consumption [3, 4] and high in both fats and sugar . Two American studies have found that African-American residents were more likely to eat a healthy diet when they had access to a local supermarket compared to smaller grocery retailers [27, 32].
Research has also determined that when living in a food desert, residents must pay higher prices for groceries at small food shops and convenience stores [33–40]. Studies in London, Ontario and the nearby Waterloo Region have found that residents will have to pay an average of 1.6 times more for identical food items purchased at area convenience stores versus area supermarkets [41, 42]. Furthermore, certain disadvantaged populations, including the elderly, disabled, unemployed, and lone-parent households, would be particularly vulnerable to the limited options in a food desert, as a function of low income and restricted mobility [7, 43, 44].
In North American cities today, the reality is that most new grocery superstores are found, along with other 'big box' outlets, in expansive retail centers which are almost always built in excess of a 500 metre walk of residential land uses, which essentially makes them accessible only to consumers with automobiles . While planners have devoted a great deal of attention in recent years to identifying the "walkability" of different built environments in relation to physical activity, and by extension obesity [45–50], critical dimensions of food environments have not received the same degree of attention [51, 52].