3.4. Classification of Thematic Maps

The thematic maps are, generally, classified into quantitative and non-quantitative maps. The quantitative maps are drawn to show the variations within the data. For example, maps depicting areas receiving more than 200 cm, 100 to 200 cm, 50 to 100 cm and less than 50 cm of rainfall are referred as quantitative maps. These maps are also called statistical maps. The non-quantitative maps, on the other hand, depict the non-measurable characteristics in the distribution of given information, such as a map showing high and low rainfall-receiving areas. These maps are also called qualitative maps.

Thematic maps are specialized maps that focus on specific themes or topics, such as rainfall, population distribution, or land use. They can be divided into two main types: quantitative maps, which illustrate measurable data (like the amount of rainfall), and non-quantitative maps, which depict qualities or characteristics that cannot be directly measured (such as areas with 'high' or 'low' rainfall). Quantitative maps are also known as statistical maps because they represent statistical data.

Think of a classroom where students are grouped by their test scores. The quantitative maps are like bar graphs showing the number of students in each score range (like 80-90, 70-80), while non-quantitative maps are like a color-coded map of the classroom showing groups labeled 'high performers', 'average'.

It would not be possible to discuss drawing these different types of thematic maps under the constraint of time. We will, therefore, confine to discuss the methods of the construction of the following types of quantitative maps: (a) Dot maps (b) Choropleth maps (c) Isopleth maps.

In this section, we focus on three specific types of quantitative thematic maps: 1. Dot maps, which use dots to represent the presence or quantity of a phenomenon in various areas; 2. Choropleth maps, which use different shades or colors to indicate the density or concentration of a particular measurement across a geographical area; 3. Isopleth maps, which connect points of equal value (like temperature or rainfall), allowing us to visualize how that variable changes over space.

Imagine you are looking at a detailed weather map of your country. The dot map indicates where the most rain falls by placing dots in those locations. The choropleth map uses shades of blue to show areas of heavy rain, while the isopleth map draws lines connecting areas that receive equal rain, just like how a weather forecaster indicates rain zones.

The dot maps are drawn to show the distribution of phenomena such as population, cattle, types of crops, etc. The dots of same size as per the chosen scale are marked over the given administrative units to highlight the patterns of distributions.

Dot maps represent the distribution of specific phenomena like population or agricultural distribution. Each dot represents a unit of measurement, such as one dot for 100,000 people. When these dots are placed over a map with administrative boundaries, they visually illustrate where that phenomenon is more concentrated or sparse.

Think of a pizza, where each slice represents a different neighborhood. If each pepperoni on the pizza is a person, then the neighborhoods with more pepperonis indicate a higher population density, just as a dot map shows denser populations with more dots.

The choropleth maps are also drawn to depict the data characteristics as they are related to the administrative units. These maps are used to represent the density of population, literacy/growth rates, sex ratio, etc.

Choropleth maps provide a visual representation of data across different regions by using varying shades or colors to indicate different levels of a measurement. For instance, a map showing literacy rates might use light colors for areas with low literacy and dark colors for areas with high literacy. This allows for a quick visual assessment of regional differences in literacy.

Imagine painting a mural for your school project. If you use light blue to represent the areas of low literacy and dark navy for the places with better literacy rates, the viewers can immediately see which areas might need more help—just like a choropleth map shows varying conditions across regions.

The word Isopleth is derived from Iso meaning equal and pleth means lines. Thus, an imaginary line, which joins the places of equal values, is referred as Isopleth. The more frequently drawn isopleths include Isotherm (equal temperature), Isobar (equal pressure), Isohyets (equal rainfall), Isonephs (equal cloudiness), Isohels (equal sunshine), contours (equal heights), Isobaths (equal depths), Isohaline (equal salinity), etc.

Isopleth maps are unique because they represent lines connecting locations that share the same value (e.g., lines connecting points with equal temperatures). This is important for visualizing phenomena that change gradually over space, such as temperature or pressure. Each line represents an equal value, such as all points at 30°C being connected by an isotherm line.

Think of a hilly landscape. If you were to draw lines on a map connecting all places that are the same height above sea level, you'd create contour lines. This is similar to how isopleth maps illustrate data, making complex information easier to understand—for instance, predicting weather patterns by connecting temperature values.

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