Generally, the objectives of a GIS are the management (acquisition, storage, maintenance), analysis (statistical, spatial modeling), and display (graphics, mapping) of geographic data. Even if a few general concepts are presented, the GIS discussed here will be seen from a health perspective. Thus, GIS will be considered as a tool to assist in health research, in health education, and in the planning, monitoring, and evaluation of health programs.
Health and ill-health are affected by a variety of life-style and environmental factors, including where people live. Characteristics of these locations (including socio-demographic and environmental exposure) offer a valuable source for epidemiological research studies on health and the environment. Health and ill-health always have a spatial dimension therefore. More than a century ago, epidemiologists and other medical scientists began to explore the potential of maps for understanding the spatial dynamics of disease.A study carried out by John Snow is often cited to show that the importance of spatial dynamics in the understanding of disease, and the use of maps to describe and analyze it, is not so recent. Dr Snow made the hypothesis that cholera might be spread by infected water supplies more than a century ago, using maps to demonstrate in a striking fashion the spatial correlation between cholera deaths and contaminated water supplies in the area of Soho in 1854.
Scholten and Lepper use the example of AIDS, stressing the importance of the spatial distribution of the disease, which they say has been too often overlooked. They cite Kabel (1990):
Modelling the spatial distribution of AIDS can contribute to both educational intervention and the planning of health care delivery systems. Mapping can play an important role in both areas as it is an excellent means of communication. In order to be of use to resource planners, predictions of AIDS should include a spatial component.
The Spatial Database
The information contained in the spatial database is held in the form of digital coordinates, which
describe the spatial features. These can be points (for example, hospitals), lines (for example,
roads), or polygons (for example, administrative districts). Normally, the different sets of data will
be held as separate layers, which can be combined in a number of different ways for analysis or
map production.
The Attribute Database
The attribute database is of a more conventional type; it contains data describing characteristics or
qualities of the spatial features: land use, type of soil, distance from the regional centre, or, using
the same examples as in the preceding paragraph, number of beds in the hospital, type of road,
population of the administrative districts. Thus, we could have health districts (polygons) and
health care centres (points) in the spatial database, and characteristics of these features in the
attribute database, for instance persons having access to clean water, number of births, number of
1 year old children fully immunized, number of health personnel, and so on.
The Image Processing System
Another source of data for a GIS is remotely sensed imagery, such as LANDSAT or SPOT
satellite imagery. A complete GIS offers tools to convert raw, remotely sensed imagery into maps.
Thus, an enormous quantity of environmental data pertinent to health can be integrated into a
health-oriented GIS (like digitizing, this task is not necessarily done by the GIS end user).
Other Data Input Methods
GIS have interfaces that permit the importation of data from numerous database or worksheet
programs. Image collection devices, such as scanners, cameras, or tape players, can also transfer
images from paper or photographic materials (maps or aerial photographs, for example) into the
GIS database.
A powerful, relational DBMS is a requisite part of a GIS for handling large quantities of information. It can provide very useful results, but a GIS must have another set of tools to give it the ability to analyze data based on their spatial characteristics. This set of tools corresponds to the geographic analysis system.
The Overlay Process
Eastman (1992) gives an example of the ability of GIS to analyze data based on their spatial
characteristics:
Perhaps the simplest example of this is to consider what happens when we are concerned with the joint occurrence of features with different geographies. For example, find all areas of residential land on bedrock types associated with radon gas. This is a problem that a traditional DBMS simply cannot solve — for the reason that bedrock types and landuse divisions simply do not share the same geography. Traditional data base query is fine so long as we are talking about attributes belonging to the same individuals. But when the entities are different it simply cannot cope. For this we need a GIS. In fact, it is this ability to compare different entities based on their common geographic occurrence that is the hallmark of GIS — a process called "overlay" since it is identical in character to overlaying transparent maps of the two entity groups on top of one another.The example given in the preceding paragraph can be developed here: Let us say we want again a map showing the districts where there is a health centre and where less than 50% of 0-1 year old children have received necessary vaccination. We want also to have on that map the hydrographic system (lakes, ponds and rivers) of the area and the location of clean water sources and sanitation utilities. We need a GIS, because the immunization data, the water and sanitation data, and the hydrographic system data have different geographies. The analytical tools available within GIS are necessary to make possible the integration of data having different geographies.
It should be noted that the geographic analysis system can contribute to the extension of the database: for example, by combining the areas where the immunization rate is low and the access to clean water is difficult, the analyst defines zones and populations at greater risk. In this way, new knowledge of relationships between features is added to the database.
Buffer Zones Creation
The overlay process is among the most fundamental aspects of a GIS, but other processes are
important and can be very useful in health research and planning.
Of particular benefit to the investigation of illness at or near pollution and other hazardous sites is the ability to create buffer zones around the lines or points which represent those locations. The user can specify the size of the buffer and then intersect or merge this information with disease incidence data to determine how many counts of the illness fall within the buffer (Twigg 1990).The association between proximity to nuclear power stations and the prevalence of childhood leukemia in northern England (Openshaw et al. 1987) has been investigated in this way, and one can easily imagine similar applications with other diseases and other environmental causes or risk factors of disease.
Buffer zones analysis can have useful applications in health services analysis and planning; for example, it gives a quick and easy answer to the question: "How many persons live within a 10 kilometre radius from this health care centre? Within a 10 to 15 kilometre radius?" The generation of a distance/proximity surface (taking into account distance and "friction" of space — resulting in a cost, in money or time, of transportation) and allocation modeling (assignment of every point of an area to the nearest of a set of designated features, for example health centres) are other geographic analysis tools that can be useful in health research and planning, where a non-spatial method could give a partial or even false answer.
For example, a GIS was used to study the difference in population per bed ratios between blacks and whites, and the implications of open access to hospital services formerly reserved for whites in Natal, South Africa. While the usual administrative boundary-based beds per capita ratios suggested that hospital bed resources in the province of Natal/Kwazulu were racially unequal but nevertheless, as expressed by Zwarenstein, Krige, Wolff (1991),
adequate (264 people per general and referred bed for the whole population, 195 for whites and 275 for Blacks), the GIS analysis reveals widespread inadequacy, worse for blacks. Of the estimated hospital catchment areas half have more than 275 black people per general and referral bed, and half of these have more than 550 black people per bed. One-third of the catchment areas estimated for whites have ratios above 275 people per bed and one half of these are also above 550 persons per bed. The GIS analysis shows that open access to beds previously reserved for whites will make no difference to rural blacks, and almost none to urban blacks, because there were relatively few such beds, and they were concentrated in the cities. For the same reasons, the opening of private hospital beds would not alleviate the apparent bed shortages in priority areas.
GIS and Health Research
By helping researchers to understand the distribution and diffusion of disease and its relationship to
environmental factors (climate, water quality, sanitation, land use, agricultural, and other
economic activities, rural-urban milieu, immunization rate, and so on), it is of value to etiology,
epidemiology, and medical science in general.
GIS and Health Education
As mapping is an excellent means of communication, GIS can be used, as Kabel (1990) suggests,
to help prepare educational material. In an article on participatory evaluation, M.T. Fuerstein
(1987) describes different methods for monitoring and evaluating community health projects,
including mapping.
Small or large maps may be drawn or painted by groups or individuals to represent the context in which they are living.... These maps, showing location of houses by number and type, public and private buildings, water sources, sanitation, bridges, roads, social centres, neighbourhood boundaries, health centres, etc. give participants a wider view of where they are living. Maps can help discussion, analysis, decision-making, management and evaluation.Fuerstein suggests that these maps be posted in a public place and updated as changes occur, providing a permanent record. GIS thus produce material that is both useful and conducive to public participation in community health projects. GIS can contribute to community development in general, by helping people understand their environment. Effects in the health domain are obvious. From this perspective, indicators developed with the people, such as the 32 indicators found in the Basic Minimum Needs (BMN) database of Thailand (Nondasuta and Chical 1988), or those measuring the 30 priority problems identified in the Recherche nationale essentielle en santé program in Bénin (Badou 1994), deserve special attention (these indicators reflect the health level as well as social, economic, and environmental key determinants of health).
GIS and Health Planning
It is evident that many questions concerning the provision of health care are related to space.
People are distributed in space and they are not evenly distributed. Health problems vary in space
and so do the needs of the people. Where should health care centres be situated and what services
should they offer to answer efficiently the needs of populations varying in numbers, densities,
and health problems? These are problems that GIS can help resolve with their spatial analysis
tools.
Maps produced by a GIS can also be used by health officials as a monitoring and evaluation tool, showing the spatial distribution and differential evolution of diseases. Monitoring and evaluation are essential parts of health programs, as well as other programs related to development. As the WHO/UNICEF Joint Monitoring Program points out (1993),
Monitoring is defined as the periodic oversight of the implementation of an activity which seeks to establish the extent to which input deliveries, work schedules, other required actions and targeted outputs are proceeding according to plan, so that timely action can be taken to correct the deficiencies detected.
Closely linked to monitoring is evaluation. Evaluation is a process by which program inputs, activities, and results are analyzed and judged explicitly against stated norms. These two terms are usually used in tandem as an integral part of every program....
Monitoring is an essential element. By giving the managers, planners and policy-makers access to information on coverage, functioning and utilization of the Water and Sanitation facilities, operation and maintenance, funding, water quality and others, monitoring as a tool guides them in making important decisions. Similarly, worthwhile evaluation of water and sanitation, as a result of effective monitoring, is necessary in ensuring rational utilization of investments allocated for the sector.It is worth noting that the second version of the WASAMS (Water and Sanitation Monitoring System) software contains a feature developed to facilitate the link with GIS. The WHO/UNICEF Joint Monitoring Program's comments on the water and sanitation program could be said, with the same words, about health programs. Monitoring and evaluation are essential parts of health programs and GIS, by showing the spatial distribution of diseases in space and time, facilitate the monitoring and appraisal of the effectiveness of health programs.
GIS is a relatively recent and complex technology, which explains why it has not been used to its full potential, especially in the health domain where it is extremely promising. We are now to a point where the possibilities are more clearly seen. Hardware and software development has produced systems with functions and interfaces which make them much easier to use. This is very good news, as GIS can certainly be a tool of prime importance to health research and education, and in the planning, monitoring, and evaluation of health programs.
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This file was created 23 February 1996