A 1,286-word essay for ENVS469 Trends Outcomes Impacts. It demonstrates the use of ArcGIS to plot the location of buildings, supermarkets, catchment areas, and population density and change. The essay received a 73, a distinction. Written in December 2016.
Supermarkets are an integral component of convenience provision, a key consideration of local planning authorities. Researchers have noted that residents without convenient access to supermarkets live in ‘food deserts’, confronting ‘significant time and transport costs when purchasing food items’ (Alviola et al, 2012). From an environmental perspective, the optimal approach to eliminating food deserts would be to minimize time and transport costs by ensuring supermarkets are within walking distance. Under this scenario, residents within walking distance might forgo driving to the supermarket, thereby reducing street congestion and greenhouse gas emissions. From a public health perspective, facilitating walking to supermarkets might increase the number of residents who meet the goal of walking 10,000 steps per day, which can lower the risk of ‘heart disease, type 2 diabetes, asthma, stroke, and some cancers’ (National Health Service, 2014).
Using ArcGIS software, this paper investigates access to supermarkets in the borough of Halton in North West England. Supermarket locations are from Geolytix, which has mapped the location of over 10,000 UK supermarkets (Bounds, 2015). An upper bound of 700 meters represents the walkable catchment area for each supermarket. That distance is less than one half-mile, which proponents of transit-oriented development argue is the maximum distance that most people will walk easily (Center for Transit Oriented Development, n.d.). To evaluate the proportion of residents living within these supermarket catchment areas, three maps were created using data from the Ordnance Survey OS VectorMap® and England’s 2011 Census at the Output Area (OA) and Middle Layer Super Output Area (MSOA) levels.
The first analysis plots Halton supermarkets and catchment areas compared to all other types of buildings in the borough (Map 2.1). Halton has 19 supermarkets, which are about evenly split between the north and south sides of the Mersey River that bisects the borough. Most supermarket catchment areas overlap—at least minimally—with at least one other catchment area, with the greatest concentration in Widnes town centre (five supermarkets).
Residents who are fortunate enough to live within each of the five Widnes catchment areas can choose between Aldi, Asda, Tesco, Iceland, and Morrisons. This variety is important, as prices can differ greatly at each brand, so specific supermarkets may be more attractive based on income (Shammas, 2016). Still, aside from a concentration of three supermarkets in the southern part of the borough, most buildings within 700 meters of a supermarket fall into a single catchment area.
Map 2.1: Halton Coverage of Supermarkets, 2015
Of those buildings outside of a catchment area, most are on the fringes of the dense northern and southern centres. Residents in these buildings would likely need to rely on a private vehicle or public transport to access a supermarket. If a vehicle is unavailable or if public transport is not convenient (e.g., infrequent), then residents in those buildings may be living in a food desert. While Halton should evaluate opportunities to bring supermarkets to these underserved areas, Map 2.1 is insufficient to make a final determination.
The next two analyses plot population density and change in Halton, because the number of potential customers is a key factor for companies deciding to open new supermarkets (Ferguson, 2013). Map 2.2 shows the same supermarket location and catchment areas, but adds 2011 population densities at the OA level.
Map 2.2: Halton Population Density, 2011
To approximate the number of residents who can walk to a supermarket, the number of residents in each OA that overlaps with a catchment area was calculated. From that amount, the number of residents without convenient access to a supermarket was derived: 32,513 (25.86% of residents). As Map 2.2 shows, many of these residents live in large, low-density parts of the borough, with fewer than 21 residents/hectare. Although several supermarkets are in low-density OAs, these are geographically small and are surrounded by much denser neighbours that are also within the catchment area.
Underserved, low-density OAs in the west and east do not benefit from nearby higher-density OAs that could potentially support a supermarket. Excluding a dense group of underserved buildings in Hale (north-west cluster in Map 2.1), these other low-density underserved areas appear to be relatively sparse. Residents in these areas may live in detached or semi-detached homes and would likely own private vehicles to drive to more distant supermarkets. Although that outcome is not good from environmental or public health perspectives, it suggests that Halton may not need to prioritise them when identifying places threatened by a lack of food access. However, offering effective public transport for them would be vital if car ownership levels are not actually high in those areas.
Map 2.2 also shows many OAs that are higher-density and are surrounded by other higher-density neighbourhoods, but are nonetheless lacking a nearby supermarket. Given that these underserved OAs have similar densities to other parts with supermarkets, Halton should consider them for new supermarkets. Still, another factor that could influence supermarket site selection is population change, i.e., a falling population may mean insufficient customers to warrant a store and vice versa.
Map 2.3 plots the population change by MSOA from 2001 to 2011. In all but six (of 17) MSOAs, Halton is experiencing population growth. Notably, four of the six areas in decline are in the southern part of the borough, including the dense, underserved areas in the south identified above as potential sites for new supermarkets. In addition, population declines in four MSOAs might risk the viability of their supermarkets if the declines persist. Still, MSOAs are far larger than OAs, so the declines may mask population growth in some already dense areas. Further, the declines are less than two per cent in four of the MSOAs, so they may only be temporary blips.
In terms of growth, the MSOA in the north with a population growth of 32.6% may warrant additional supermarkets, to accommodate the additional residents. The same may be true for the MSOAs with growth of 20.2 and 22.2%.
The three analyses suggest that a majority of Halton residents live within walking distance of a supermarket. They also help to indicate which areas are not only underserved, but which could potentially support a new supermarket. However, features of the analyses could both under and overestimate access to supermarkets. For example, the analyses exclude supermarkets in the local authorities that surround Halton. Residents living near the border would be in their catchment areas. In addition, the population determined to live within 700 meters of a supermarket is an overstatement because the analysis includes all residents in an OA even if only part of the OA is in the supermarket catchment area.
Within Halton, the catchment areas do not account for the Mersey River. In one instance, the analysis counts residents living in across the Mersey from a supermarket as within the catchment area. Living within a catchment area also does not guarantee a safe or direct route (e.g., due to lack of pavements).
Considering other variables could also enhance the analysis. For example, demographic data could help to avoid overstating the accessibility of supermarkets, particularly if shorter walks are more realistic for a cluster of residents within the catchment area (e.g., the elderly). In addition, socioeconomic data can highlight areas to prioritise, especially since lower income people may not be able to afford a car to drive to distant supermarkets. Further, additional years of data could reveal whether supermarkets closed recently in currently underserved areas as well as longer-term trends in population density and growth.
While the provision of supermarkets is important, their location is not the only solution to food deserts. Instead of looking at supermarkets alone, Halton could explore the ‘Healthy Corners’ strategy from Washington, DC, which has increased the availability of fresh fruits and vegetables at convenience stores in underserved areas, or devise its own novel approach (Sidman, 2014).
Alviola, P.A., Nayga Jr., R.M., and Thomsen, M. (2012). ‘Food deserts and childhood obesity’, Applied Economic Perspectives and Policy, doi: 10.1093/aepp/pps035.
Bounds, A. (2015). ‘UK open data revolution boosts business’, Financial Times, 1 June. Available at: https://www.ft.com/content/22b3afc4-0600-11e5-868c-00144feabdc0
Center for Transit-Oriented Development. (n.d.). Why transit-oriented development and why now? Available at: file://ufs02/user02/SGJALVES/Desktop10/tod101.pdf (accessed 11 November 2016).
Ferguson, D. (2013). ‘How supermarkets get your data – and what they do with it’, The Guardian, 8 June. Available at: https://www.theguardian.com/money/2013/jun/08/supermarkets-get-your-data (accessed 14 November 2016).
National Health Service. (2014). Walking for health. Available at: http://www.nhs.uk/livewell/getting-started-guides/pages/getting-started-walking.aspx (accessed 11 November 2016).
Shammas, J. (2016). ‘Britain’s “cheapest” supermarket revealed after year-long study – and the results may surprise you’, Mirror, 4 January. Available at: http://www.mirror.co.uk/news/uk-news/britains-cheapest-supermarket-revealed-after-7101472 (accessed 11 November 2016).
Sidman, J. (2014). ‘D.C. corner stores aren’t just for junk food anymore’, Washington City Paper, 27 February. Available at: http://www.washingtoncitypaper.com/food/blog/13130775/d-c-corner-stores-arent-just-for-junk-food-anymore (accessed 14 November 2016).