Summary: Distributional Maps
Ordinary maps mainly tell us where places are. Thematic maps go a step further: each one is drawn around a single theme, such as rainfall, temperature or population, and shows how that variable is spread over a region. Distributional maps are thematic maps built from statistical data.
In the dot method, every dot stands for a fixed count, for example 1 dot = 10,000 people. Only counted data is used. Dots must all be the same size, and they are placed with care, keeping hills, rivers, roads and towns in mind. Rural population is shown with dots and big towns with circles.
In the choropleth method, each sub-administrative unit (such as a taluka) gets one value and is filled with one shade. The data is grouped into 5–7 classes; a higher class gets a darker shade of the same colour, or a denser black-and-white pattern.
In the isopleth method, lines join places that have the same value of a continuous variable, like height, temperature or rainfall. Data belongs to points (places), not to units. Lines close together show a quick change; lines far apart show a gentle change.
A field visit lets us see geography first-hand. It needs planning (place, purpose, route, questionnaire, permission), safety rules during the visit, and a written report with maps, photographs and conclusions.
Key points to remember
- Thematic maps show one theme; distributional maps show how a variable is spread over a region
- Three methods: dot, choropleth and isopleth
- Dot method uses counted data only — population, cattle, number of animals
- Decide the value of one dot from the lowest and highest values in the data
- All dots must be of equal size; place them according to relief, water and roads
- Rural population → dots; urban population → circles
- Choropleth: one value per administrative unit, 5–7 classes, darker shade = higher value
- Choropleth suits density, production per taluka, literacy rate and similar ratio data
- Isopleth: lines of equal value for continuous data such as altitude, temperature, rainfall
- Isopleth data is point-related; administrative boundaries are ignored
- Close isolines = steep change; widely spaced isolines = gentle change
- A field-visit report has an introduction, maps, physiography, climate, population, land use, problems and conclusions
