Thematic maps: requirements, rules and classes

Detail

Why we need thematic maps

• Graphs and diagrams (line graphs, bar diagrams, pie diagrams) are good for comparing values, such as the population of five states.
• They have one weakness: they give no regional perspective. A bar for "Bihar" does not show where the dense parts of Bihar are, or how Bihar compares with the states around it.
• A thematic map fixes this. It is also called a distribution map.
• Definition: a map that shows the spatial pattern (how something is spread over an area) of one or a few themes over a base map.
• Theme: the single subject the map is about, such as population density, rainfall or literacy.

• Base map: the plain background map (outline, boundaries) on which the theme is drawn.

• Class 6 NCERT (Locating Places on the Earth) calls these maps that show one specific kind of information. Examples are maps of roads, rainfall, forests or industries.

• Class 11 NCERT (Introduction to Maps, Practical Work) shows a series of thematic maps of Nagpur district (Maharashtra). Each map in the series shows a different theme for the same area.

Who makes thematic maps in India

• NATMO (National Atlas and Thematic Mapping Organisation) is India's main agency for thematic maps and atlases. Its headquarters is in Kolkata [2][3].
• It began in 1956 as the National Atlas Organisation, after Jawaharlal Nehru approved it. Prof. S. P. Chatterjee led it [2][3].
• It was renamed NATMO in 1978 and given wider work in thematic cartography and geographical research [2].
• It works under the Department of Science & Technology (DST), Government of India, as an Attached Office [2][3].
• Its first major product was India's first National Atlas, the Bharat Rashtriya Atlas (Hindi version), made in nine months [3].
• Output: 100+ atlases, 500+ thematic maps and about 200 monographs. These include agricultural, environmental, health and disease, climatic-region, natural-hazard and land-use maps, plus an atlas for visually impaired people (Braille) [2][3].

• Its geo-portal 'Manchitran' gives free digital access to e-Atlases, PDF maps and geospatial layers. It was launched within six months of the government freeing up the collection and sharing of geospatial data [3].

• NRSC / ISRO (Bhuvan portal) makes thematic maps from satellite images (see the land-use example below) [4][5].

Requirements for making a thematic map

To draw a thematic map you need three things:

Requirement	What it gives you	Example
State- or district-level data on the theme	The numbers to be mapped	District-wise population density from the Census
Outline map with administrative boundaries	The units (states, districts) into which data are filled	India map showing district borders
Physical map of the region	Ground conditions that explain the pattern	Physiography (landforms) for a population map; relief and drainage (heights and rivers) for a transport map

• Why a physical map is needed:
• People settle thickly on plains and thinly on hills and deserts. A relief map helps place population dots correctly.
• Roads and railways follow valleys and avoid steep slopes and big rivers. Relief and drainage maps explain the transport network.

Rules for making a thematic map

Every thematic map must show:

1. Name of the area shown (for example, "India" or "Nagpur district").
2. Title of the subject (for example, "Population Density, 2011").
3. Source of data and the year (for example, "Census of India, 2011").
4. Symbols, signs, colours and shades used, explained in a legend (key).
5. Scale of the map.
6. A suitable method of showing the data. Choose dot, choropleth or isopleth depending on the kind of data.

Classification by method of construction

Thematic maps are grouped by how the data are shown:

Class	Other name	What it shows	Example
Quantitative map	Statistical map	Measurable variations, shown as numbers or class ranges	Rainfall shown as >200 cm, 100–200 cm, 50–100 cm, <50 cm
Qualitative map	Non-quantitative map	Features that cannot be measured in numbers, only named or described	Only "high" and "low" rainfall areas; land use types (forest, cropland, built-up)

• Trap: the same theme (rainfall) can be either kind. It depends on whether it is mapped with measured class ranges (quantitative) or with descriptive labels (qualitative).
• A real qualitative map: Bhuvan land use / land cover (LULC)
• NRSC has mapped LULC across India at 1:50,000 scale for 2005–06, 2011–12 and 2015–16 [4][5].
• The third cycle (2015–16) used images from Resourcesat-2 LISS-III, taken in three seasons [5].
• It used a 54-class scheme, which was reduced to 24 classes for sharing on Bhuvan [5].
• Other Bhuvan thematic layers at 1:50,000 include wasteland, geomorphology and lineament maps [4].
• These layers are shared as WMS/WMTS web services (standard formats that let other mapping software display them) [4].

The three quantitative methods NCERT constructs

NCERT constructs three quantitative types:

Method	How it works	Best for
Dot map	Each dot stands for a fixed number (e.g. 1 dot = 10,000 persons), placed where the thing occurs	Population (human and livestock), crop-growing areas
Choropleth map	Administrative units are shaded; darker shade = higher value	Ratios and densities by state or district: population density, literacy
Isopleth map	Lines join places with the same value	Values that change smoothly across space: temperature, pressure, rainfall

• Isopleth (a line on a map joining points where a variable has the same value) [6]. Common kinds are the isotherm (equal temperature), isobar (equal pressure), isohyet (equal rainfall) and contour (equal height).

Prelims Hooks

• Thematic map = distribution map: one or a few themes drawn over a base map.
• Graphs and diagrams lack a regional perspective. Thematic maps supply it.
• Physical map needed: physiography → population map; relief and drainage → transport map.
• Compulsory parts: area name, subject title, data source and year, symbols and shades (legend), scale.
• Quantitative = statistical (measurable). Qualitative = non-quantitative (not measurable). Land use type map = qualitative.
• Rainfall in ranges (>200 cm … <50 cm) = quantitative. "High/low rainfall" = qualitative.
• NCERT's three quantitative methods: dot, choropleth, isopleth.
• NATMO: set up 1956, renamed 1978, HQ Kolkata, under DST. Geo-portal Manchitran [2][3].
• First National Atlas: Bharat Rashtriya Atlas (Hindi), made by NATMO [3].
• Bhuvan LULC: 1:50,000 scale, three cycles (2005–06, 2011–12, 2015–16), Resourcesat-2 LISS-III data, 54 → 24 classes [4][5].

Mains Points

• Thematic maps support planning (GS-I, GS-III): district-level maps of population, literacy, land use and hazards show where to place schools, irrigation and disaster shelters. NATMO's District Planning Map Series and natural-hazard maps serve this purpose [2].
• From paper to digital: satellite-based LULC mapping by NRSC is repeated over time (2005–06, 2011–12, 2015–16). Comparing cycles shows change such as cities growing or forests shrinking. Free portals (Manchitran, Bhuvan) open this data to citizens and researchers [3][4][5].
• Choosing the method matters: choropleth maps hide differences inside a district. Dot maps show clustering. Isopleths suit continuous data like rainfall. A wrong choice can mislead policy. This is why the rules require the source, year and legend to be shown.
• Inclusive cartography: NATMO's Braille atlas for visually impaired people shows that maps can be made accessible to everyone [2].