Many people are fascinated by maps, and most find them useful, though not in all situations. A lone driver, without a map-reading navigator, will find it difficult to use a map. More recent in-car navigation systems are designed to help such a driver, or one who is without map-reading skills but is able to follow directions.
This section uses maps to introduce some important terms and concepts. It also examines a navigation system, used both in cars and in hand-held devices, as an example of the application of computer systems to problem solving.
Maps use latitude and longitude to form a two-dimensional grid that covers the curved surface of the earth.
Altitude or depth (based on a notional sea level) can be superimposed on the latitude and longitude grid using lines connecting adjacent points of the same altitude or depth, called contour lines. Contour lines give a map-reader (using a two-dimensional map) an idea of the topography of the area covered by the map.
A map showing only latitude, longitude and contour lines might be of great interest to a geographer. But such a map would be almost useless for, say, a rambler or a driver unless other features, such as roads and villages, were also shown on the map. Examples of two types of map are shown in Figures 8 and 9. Both cover approximately the same area but look very different. They are for a similar purpose (longer distance travel) but serve completely different audiences.
Maps can be made up of separate layers of data. The idea of layering can best be understood if you imagine that each of the following layers is printed on transparent overlays, except the first (the grid) which is printed on opaque paper:
- the underlying grid of latitude and longitude
- contour lines showing altitude
- features such as rivers, roads, buildings and boundaries
- the names of towns, roads, hills, rivers and other notable features of the landscape.
Other types of map may have quite different layers. For example, part of a map showing the incidence of cholera is shown in Figure 10. This was produced by Dr John Snow in 1854, and is a classic example of medical cartography, as it proved that cholera was a water-borne disease.
The layers in this map consist of: (1) the relevant 1854 London streets, (2) the location of 578 deaths from cholera and (3) the position of 13 water pumps. Each location of a death specifies the address of a person who died from cholera. When many such locations are associated with a single address, they are ‘stacked’ in a line away from the street so that the numbers of deaths at an address are more easily visualised. (Using this mapping technique, Dr Snow identified a contaminated pump as the source of the cholera outbreak. By removing the handle of the pump once he’d identified it, Dr Snow averted an epidemic.)
Early maps were drawn using counted paces, and local knowledge for place and feature names. However, as the need for greater accuracy grew, geographical data began to be gathered by a painstaking and exacting process of measurement carried out by surveyors. The tools used in the task included chains of an exact length, accurate clocks, sextants and theodolites. Modern mapping still uses some of these, but also relies on aerial photography, on remote sensing from orbiting satellites (described earlier in Example 3) and, increasingly, on the global positioning system (GPS).
This GPS technology can and does have potential use within the healthcare domain. This can include tracking assets such as beds, thus allowing hospitals to know where these may be at any one time (storage, moved to another ward, in a corridor, etc.) to geofencing solutions, that allow families and professionals to set boundaries for clients that send an alert if they stray beyond predefined geographical fences. This is potentially of use when caring for patients with dementia, who may at time wander, with a small wearable device that can be tracked when they cross the threshold set in consultation with them and their relatives. Obviously, issues around surveillance and potential deprivation of liberty may need to be addressed – but the use of technology within an appropriate regulatory framework offers solutions for care unimaginable in the 20th century.