John Snow's cholera map of London in 1854 is a classic example of a qualitative map. It highlighted the spatial distribution of cholera cases to identify the source of the outbreak.
Understanding Qualitative Maps
Unlike quantitative maps that display numerical data, qualitative maps focus on showing the types of features present rather than their quantity or magnitude. They illustrate the spatial arrangement of phenomena based on categories or characteristics. The goal is often to reveal patterns and relationships.
John Snow's Cholera Map: A Detailed Look
- Purpose: The primary aim was to pinpoint the source of the cholera outbreak in the Broad Street area of London.
- Data Representation: Snow marked the locations of cholera deaths with small bars on a map of the area.
- Key Finding: By visually analyzing the map, Snow observed that a large number of cases clustered around a particular public water pump on Broad Street.
- Impact: Snow's map provided compelling visual evidence that contaminated water from the Broad Street pump was the likely source of the outbreak. Removing the pump handle dramatically reduced the number of new cases, confirming his hypothesis.
- Why It's Qualitative: The map depicted the presence of cholera cases at different locations rather than quantifying aspects like the rate or severity of the illness, making it a prime example of a qualitative map.
- Significance: It's an early example of using geographic data to support a hypothesis and influence public health policy.
Other Examples of Qualitative Maps:
While John Snow's map is a famous example, qualitative maps can be used in various other contexts:
- Land Use Maps: Showing different types of land use, such as residential, commercial, industrial, or agricultural areas.
- Geological Maps: Displaying different types of rock formations or soil.
- Vegetation Maps: Illustrating the distribution of various plant communities.
- Political Maps: Showing the boundaries of countries, states, or provinces.
