Graphical Representation of Data Class 12 NCERT Solutions

Each MCQ pairs one map or graph type with its defining feature. Dot maps show distribution (where things are); choropleth maps show density or rate (how much per unit); isopleth maps join points of equal value; flow maps show movement and are therefore the dynamic family. Line graphs are the standard choice for time-series data. Polygraphs plot several variables on the same axes, so they need more than two variables to be useful.

• (i) Population distribution map. Distribution means "where the population is", and that is exactly what a dot map shows: one dot represents a chosen unit of population, scattered to match real spread. Choropleth shades a whole unit (showing density, not distribution). Answer: (c) Dot maps.
• (ii) Best for decadal growth. Decadal growth is a time-series (one observation per decade). The natural choice is a line graph that lets you see the rise and fall over time. Answer: (a) Line graph.
• (iii) Polygraph variables. A polygraph plots two or more series on the same axes to compare them. More than two variables is the purpose of a polygraph. Answer: (c) More than two variables.
• (iv) Dynamic map. A flow map uses arrows to show movement (traffic, migration, trade). Movement implies dynamics; the chapter therefore labels the flow map as the dynamic map. Answer: (d) Flow map.

(i) (c) Dot maps; (ii) (a) Line graph; (iii) (c) More than two variables; (iv) (d) Flow map.

A thematic map shows a single theme (population, rainfall, soil) on a base outline. Multiple bar diagrams place bars for each variable side by side; compound bars stack the components into one bar. Dot maps need a base map, the data set, a dot value, a key, and smart placement. Traffic flow maps use proportional-width arrows on the route network.

• (i) Thematic map, defined. A thematic map shows the distribution of a single theme (population, rainfall, literacy, soil types) on a base map. Unlike a general-purpose map, a thematic map foregrounds one variable at a time.
• (ii) Multiple bar vs Compound bar. A multiple bar diagram places bars for each component side by side within a category, so the eye can compare components. A compound bar diagram stacks components into one bar per category, so the total height also reads off alongside each component's share.
• (iii) Requirements to construct a dot map. (a) A base map with administrative boundaries. (b) Data values per unit. (c) A chosen dot value (for example, 1 dot = 5,000 people). (d) A legend explaining the dot value. (e) A placement strategy that puts dots where the variable actually concentrates, not spread uniformly.
• (iv) Constructing a traffic flow map. Take a base map of the road or rail network. Collect traffic-volume data per segment. Choose a width scale. Draw arrows along each segment with width proportional to its traffic value. Add direction arrows, a legend, title, scale, north arrow and source.

Thematic map: single theme on a base outline. Multiple bar: components side-by-side. Compound bar: components stacked into one total bar. Dot map needs base map, data, dot value, legend, smart placement. Traffic flow map = proportional-width arrows along the route network with direction and legend.

An isopleth map joins points of equal value of a variable using curves (isobars for pressure, isotherms for temperature, isohyets for rainfall, contours for height). Interpolation estimates the position of an iso-value between two observed points by linear proportional reasoning. A choropleth map fills administrative units with shades that match a chosen class of the variable. A pie diagram divides a circle into slices whose angles are proportional to the component values.

• (i) Isopleth map and interpolation. An isopleth map shows the distribution of a continuous variable (rainfall, temperature, pressure, elevation) by joining points with the same value through smooth curves. Each curve is called an isoline. Common types: isobars (pressure), isotherms (temperature), isohyets (rainfall), contour lines (elevation). Interpolation method: Suppose station A records 1000 mm of rain and station B, 200 km away, records 1400 mm. To locate the 1200 mm isohyet between them, assume linear change: (1200 - 1000) = 200; total range (1400 - 1000) = 400; fraction = 200 / 400 = 0.5. So the 1200 mm line is at 0.5 x 200 = 100 km from A. Apply the same logic to every pair of neighbouring stations and join the resulting points to draw the isoline.
• (ii) Steps to prepare a choropleth map. Step 1. Collect data for each administrative unit. Step 2. Compute the chosen ratio or density (population per sq km, literacy rate) so all values are comparable. Step 3. Arrange the data into 4-6 classes (equal interval, quantile or natural-break method). Step 4. Choose a colour ramp: light shades for low values and dark shades for high values. Step 5. Trace the base map with all administrative boundaries clearly. Step 6. Fill each unit with the shade of its class. Step 7. Add legend (showing class ranges and shades), title, north arrow, scale and source.
• (iii) Steps to draw a pie diagram. Step 1. List the component values and total. Step 2. Compute each component's percentage of the total. Step 3. Convert each percentage into a slice angle: angle = (component value / total) x 360 degrees. Step 4. Draw a circle of suitable size. Step 5. Use a protractor to mark the angles starting from the 12 o'clock position; draw the slice boundaries. Step 6. Shade or colour each slice differently and label. Step 7. Add a title, legend and source. Example: If a household spends Rs 6000 on food, Rs 3000 on rent and Rs 3000 on others (total Rs 12000), the slices are 180 degrees, 90 degrees and 90 degrees respectively.

Isopleth map joins points of equal value using interpolation between observed stations. Choropleth steps: collect data, normalise, classify, choose colour ramp, draw base, fill units, add legend. Pie diagram steps: list values, compute percentages, convert to angles, draw circle, mark with protractor, label.