2.2 SPATIAL ANALYSIS AND PUBLIC HEALTH

2.2 SPATIAL ANALYSIS AND PUBLIC HEALTH

The conception that we have of GIS nowadays began to emerge in the 1960s, with the

development of computerized map systems and the launch of remote sensing satellites of

the Earth's surface. According to Smith et al. (2021, ¶ 2),

The term ‘GIS’ is widely attributed to Roger Tomlinson and colleagues, who used it in 1963 to describe their activities in building a digital natural resource inventory

system for Canada (Tomlinson 1967, 1970). The history of the field has been charted

in an edited volume by Foresman (1998) containing contributions by many of its

early protagonists. A timeline of many of the formative influences upon the field is

provided in Longley et al. (2015, p. 20). The research makes the unassailable point

that the success of GIS as an area of activity has been driven by the success of its

applications in solving real world problems.

Previous to the conception of GIS, but nonetheless part of its nature is spatial analysis,

which can answer several questions related to data that have a geographical component.

The table below (Figure 3) provides some examples of the types of questions that may

appear in spatial analysis.

Analysis General Question Example

Condition

What is...? What is the population of this city? What are the areas with a slope above Localization Where is...? 20%?

Trend What has changed...? Was this land productive five years ago?

Routing Where to go...? What is the best way to the subway?

Pattern What is the pattern...? What is the distribution of dengue (disease) in Fortaleza?

Model What happens if...? What is the impact on the climate if we deforest the Amazon?

Figure 3. Spatial Analysis. Adapted from INPE, 2006.

In the health care field, these questions can also be asked to answer, for example, who fell

ill, and where or when the disease occurred (Hino et al., 2006).

The spatial analysis conducted by John Snow in 1854, aiming to study the relationship

between the occurrence of cholera in London and the supply of water in different supply

pumps in the city (Snow, 1999), is a classic study of spatial analysis and can also be applied

to public health. By mapping the locations of cholera deaths and whether the water supply

came from a collection point upstream or downstream of the sewage discharge into the

River Thames (Figure 4), Snow was able to demonstrate the relationship between the

disease and water contamination conclusively.

Figure 4. John Snow’s map of cholera cases in London. Adapted from Tufte, 1983 apud INPE, 2006.

The applications of GIS in public health are diverse, especially in the field of epidemiology,

where geographic information can be used to search for causes and effects related to the

health of the population (León, 2007).

One of the main approaches of mapping in epidemiology is identifying risks according to

geographic regions, merging information related to the frequency of occurrence, spatial

distribution, and factors that offer health hazard and that do not have a homogeneous

distribution in all social groups. Knowledge of this information is essential to reduce or

eliminate the health risks to a specific population and, in a preventive sense, avert the

emergence of dangerous situations in public health.

According to the Ministério da Saúde (2006), the main applications of spatial analysis in

public health are:

- Disease mapping, through the construction of maps of epidemiological indicators;

- Ecological studies, measuring the association between aggregated indicators;

- Health and environment, relating different layers of data on environment and

health;

- Detection of clusters, identifying clusters related to the highest incidence of

diseases and variables of interest;

- Diffusion processes, evaluating the evolution of the spatial distribution of diseases

in time and space;

- Study of trajectory between locations, aiming to analyze health care networks;

Going further, these analyses can be grouped into three major fields of knowledge (Figure

5), assisting in the planning, evaluation, and monitoring of programs implemented in public

health and decision-making by politicians and managers.

pidemiologicalSurveillance ealth Services valua on

Spa al distribu on of diseases and determina on of pa erns elimita onof ris areas apping of basic health indicators nalysis of research hypotheses from the understanding of di usion and e posure to speci c agents lanning of disease preven on and control ac vi es.

nalysis of the spa al distribu on of health services lanning and op mi a on of health resources ccessibilitystudy se of health services nalysis of the pa ent ow to determine areas of demand for health resources. rban disease ecology Study of social, demographic and environmental factors in ci es nalysis of how pollu on, overpopula on, stress and poverty a ect human health in ci es i erences in the use of space by di erent social groups due to economic and poli cal pressures on society.

rbani a onand nvironment

Figure 5. Fields of application of GIS in Public Health. Adapted from RIPSA, 2000 apud León, 2007.

These possibilities of using GIS in public health allow essential questions to be answered to

understand important phenomena in the field of health surveillance (Ministério da Saúde,

2006), such as

• what is the pattern of case distribution of a disease in space;

• whether there is any relationship between a disease, possible sources of

contamination, or means of dissemination;

• what is the evidence about the transmissibility of a disease, whether it is

transmitted from individual to individual or through a common source.

Regarding the methods used in the spatial analysis of information related to public health,

according to Hino et al. (2006), they can be divided into:

- Visualization: the mapping of health events is the primary tool, ranging from the

point distribution of events to complex overlays of disease incidence maps which

describe the distribution of certain variables of interest.