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Data: Source and Compilation (Class 12 Geography Practical)

Data are numbers or facts about places and people. We get them from primary sources (our own field work), secondary sources (published by others) and unpublished records. Raw data are messy, so we tabulate them in a clear table, group them into equal classes and count the frequency of each class. A frequency polygon joins the midpoints of the classes to show the shape of the data.

🎬 Step-by-step story

  1. Data come from three places: primary (you collect it), secondary (already published), unpublished (office records).
  2. Raw data is a messy list. Tabulation puts it into rows and columns with a title, headings and units.
  3. Grouping: make equal classes, put a tally for each value, count it. That count is the frequency.
  4. Draw each class as a bar with no gaps (a histogram): width = class interval, height = frequency.
  5. Frequency polygon: join the midpoints of the bar tops, adding a zero class at each end.
  6. Try it: change the class width and see how the table and the polygon change.

Tip: drag the 3D scene to turn it. Use two fingers to zoom.

🤔 Common doubts, cleared

Is data from a website primary or secondary?

Secondary, because someone else collected and published it. It becomes primary only if you collected it yourself.

Why can't I just keep the raw list?

A long list is hard to read. A table shows the same numbers in order, with headings and units, so you can compare quickly.

Where does a value exactly on the class boundary go?

In the exclusive method it goes to the class where it is the lower limit: 20 goes to 20–30.

What is the difference between a histogram and a bar diagram?

A histogram has no gaps because the classes are continuous. A bar diagram has gaps because items are separate (like crops).

Why use midpoints for the polygon?

The midpoint stands for the whole class. It is the fairest single point to represent all values in that class.

How many classes should I make?

Usually 5 to 15. Too few hide the pattern; too many make it jumpy. Try it with the slider.

What are data and why do geographers need them?

Data are numbers or facts we record, such as rainfall, crop output or the number of people in a village. Geographers use data to compare places, find patterns and plan (roads, schools, water).

Data can be about quantity (how much, how many) or quality (type of soil, type of house).

Sources of data: primary, secondary and unpublished

Primary sources

Data you collect yourself, first-hand. Methods: personal observation (look and record), interview (talk to people), questionnaire or schedule (a printed list of questions), and other methods like measuring soil or water in the field.

Secondary sources

Data someone else collected and published. Examples: Census of India, National Sample Survey, weather reports, government yearbooks, maps, books, journals, newspapers, international reports (UN, World Bank) and official websites.

Unpublished sources

Records kept by offices but not printed for the public: village land records (patwari), municipal files, school registers, hospital records, company files.

Which is better?

Primary data fit your exact question but take time and money. Secondary data are quick and cover large areas, but may be old or collected for another purpose.

Tabulation: putting data into a table

Tabulation means arranging data in rows and columns. A good table has a number, a title, column headings, units (cm, km², %), the body with the values, and the source at the bottom.

Tables make big data easy to read and compare. You can also add totals, averages and percentages. Absolute numbers, ratios and percentages can all be tabulated.

Grouping data into classes

When there are many values, we group them into classes (like 0–10, 10–20). Each class has a lower limit and an upper limit. The difference is the class interval (class width).

Steps

  1. Find the range = highest − lowest value.
  2. Choose the number of classes (usually 5 to 15) and a round class width.
  3. Put a tally mark for each value in its class (every fifth mark crosses the four: ||||).
  4. Count the tallies. This is the frequency (f). The frequencies must add up to the total number of values (N).

Exclusive and inclusive methods

Exclusive: 0–10, 10–20… the upper limit is not included, so 10 goes to 10–20. Inclusive: 0–9, 10–19… both limits are included. Cumulative frequency is the running total of frequencies.

Frequency polygon

A frequency polygon is a line graph of grouped data. Steps:

  1. Find the midpoint of each class: (lower + upper) ÷ 2.
  2. Plot midpoint on the x-axis and frequency on the y-axis.
  3. Add one extra class with frequency 0 at each end, so the shape closes on the x-axis.
  4. Join the points with straight lines.

You can draw it on top of a histogram (joining the midpoints of the bar tops) or alone. Two polygons on one graph help compare two sets of data. An ogive is a similar line for cumulative frequency.

Key formulas and definitions

Worked examples

1. You count the vehicles passing your school gate for one hour. Is this primary or secondary data?

Primary. You collected it yourself by observation.

2. Data taken from the Census of India report to compare literacy of two districts: what type?

Secondary data, because it was collected and published by the Census office.

3. Values range from 12 to 87. You want 8 classes. What class width should you choose?

Range = 87 − 12 = 75. 75 ÷ 8 ≈ 9.4, so round up to 10. Classes: 10–20, 20–30, …, 80–90 (8 classes).

4. Find the midpoints of classes 20–30, 30–40 and 40–50.

(20+30)/2 = 25, (30+40)/2 = 35, (40+50)/2 = 45.

5. Rainfall values: 12, 25, 7, 31, 18, 22, 9, 27, 15, 34, 21, 13, 28, 19, 5, 24, 16, 38, 23, 11 (cm). Group them in classes of 10 (exclusive).

0–10: 7, 9, 5 → f = 3. 10–20: 12, 18, 15, 13, 19, 16, 11 → f = 7. 20–30: 25, 22, 27, 21, 28, 24, 23 → f = 7. 30–40: 31, 34, 38 → f = 3. Check: 3+7+7+3 = 20 = N.

6. Using the table above, list the points you plot for the frequency polygon.

Add empty classes −10–0 and 40–50 with f = 0. Points (midpoint, f): (−5, 0), (5, 3), (15, 7), (25, 7), (35, 3), (45, 0). Join them with straight lines.

7. Convert the inclusive classes 10–19, 20–29, 30–39 to exclusive classes.

Gap between 19 and 20 is 1; half is 0.5. Subtract 0.5 from lower limits and add 0.5 to upper limits: 9.5–19.5, 19.5–29.5, 29.5–39.5.

Common mistakes

Practice quiz

1. Data collected by interviewing farmers yourself are:
2. Which is a secondary source?
3. The midpoint of class 40–60 is:
4. In the exclusive method, the value 30 goes into:
5. A frequency polygon is drawn by joining:

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Frequently asked questions

What are the sources of data in Class 12 Geography?

Primary sources (personal observation, interview, questionnaire/schedule, field measurement), secondary sources (published: Census, surveys, reports, maps, websites) and unpublished records (office files, registers).

What is a frequency polygon?

A closed line graph made by plotting class midpoints against frequencies and joining them with straight lines, with a zero class added at both ends.

What is the difference between inclusive and exclusive class intervals?

In exclusive classes (0–10, 10–20) the upper limit is not included. In inclusive classes (0–9, 10–19) both limits are included.

Where this is taught

Spain2º ESOScientific project
Spain3º ESOScientific project
Spain4º ESOScientific project
CBSE (India)Class 12Practical Work in Geography Part II

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