Introduction to Geography
Senior 1 · Geography
Introduction to Geography
Lesson 3 of 3
22 min
The image below was not drawn by anyone. A camera on a NASA satellite recorded it from about 700 km above the Earth. Look at it for one minute. Find Lake Kivu, the clouds and the black border lines, and decide what the brown streaks near the centre might be.
A single image shows the shape of lakes and rivers, where forest and farmland are, and where towns have spread. It covers the whole country at once, which no field trip could do. But it cannot tell you what crop a farmer grows, how much she earns, or why she moved there. Clouds can also hide the ground; this image was taken in May, near the end of the long rainy season, and much of the north is covered.
So geographers never rely on one source. They combine information they collect themselves with information collected by others.
Definition
Primary source (primary data): information you collect yourself, first-hand, for your own purpose: by observing, measuring, counting, photographing or asking people. Example: counting the vehicles that pass your school gate in 10 minutes.
Definition
Secondary source (secondary data): information that someone else collected and that you use afterwards: maps, atlases, books, statistics, reports, newspapers, radio, television, websites and satellite images. Example: the population of your district taken from the 2022 census report.
Definition
Fieldwork: studying geography outside the classroom, where the features and people actually are, in order to collect primary data. Example: visiting a nearby stream to measure its width and depth and to record what is dumped along its banks.
Figure 1. A rain gauge collects primary data. Each morning the water is poured into the measuring cylinder, read in millimetres, and the bottle is emptied.
Good fieldwork follows five steps: (1) ask a clear question, such as "Is the stream below our school polluted?"; (2) plan what to measure, where and when, and how to stay safe; (3) collect the data in the field; (4) present it in tables, graphs, maps and photographs; (5) conclude by answering the question and saying what could be improved.
Worked example: from readings to a result
A class in Musanze reads its rain gauge every morning for one week and records (in mm): 12, 0, 5, 23, 0, 8, 1. Find the total rainfall and the mean daily rainfall.
Step 1. Total. mm.
Step 2. Mean.
Step 3. Interpret. Most of the week's rain fell on one day (23 mm), and two days were dry. The mean hides this, so a bar graph of the daily readings shows the pattern better than the mean alone.
| Source | Rwandan example | Strength | Limitation |
|---|---|---|---|
| Maps and atlases | A map of Rwanda's districts | Show where things are at a glance | Can be out of date; small-scale maps leave out detail |
| Statistics | The 2022 census by the National Institute of Statistics of Rwanda (NISR) | Cover the whole country, collected carefully | Collected only every ten years; averages hide differences |
| Weather records | Rainfall and temperature data from Meteo Rwanda | Many years of measurements | Stations are far apart; your valley may differ |
| Books and reports | Your Student's Book; environment reports by REMA | Explain as well as describe | May be written for another country or an older time |
| Radio, TV, newspapers | A news report on floods in the Western Province | Up to date | May be short, dramatic or one-sided |
| Internet | Government and university websites | Fast; huge amount | Anyone can publish; check who wrote it and when |
| Satellite images and aerial photographs | The images in this lesson | Show large or hard-to-reach areas; can be repeated to show change | Clouds; need skill to interpret; cannot show people's reasons |
Definition
Remote sensing: collecting information about the Earth's surface from a distance, without touching it, usually by cameras and sensors on satellites or aircraft. A picture produced this way is a satellite image (from space) or an aerial photograph (from an aircraft or drone). Example: using satellite images taken years apart to measure how much forest has been cleared.
STEMonstrations: Earth Science Remote Sensing, by Learn With NASA (4 min). Watch for the difference between a passive sensor (a camera using sunlight) and an active one (a sensor that sends out its own signal).
Important
Case study: Rwanda's 2022 census, a primary source that becomes secondary
In August 2022 enumerators working for NISR visited every household in Rwanda and recorded who lived there, their ages, schooling, work and housing. It was Rwanda's fifth census, after those of 1978, 1991, 2002 and 2012. The results, 13,246,394 people, are used to decide where new schools, health centres and roads are most needed.
For NISR the census is primary data: they collected it themselves. When you read the census report to find your district's population, it is a secondary source for you. Whether a source is primary or secondary depends on who collected it and for what purpose.
Warning
Check before you trust. For any secondary source ask: Who made it? When? How was it collected? Does it agree with another source? A 2002 satellite image cannot show a road built in 2020.
Your sector has opened a new market, and people say traffic at the nearby junction has got worse. Plan how you would find out whether this is true. Name two primary sources and one secondary source you would use, and explain why you need both kinds.
Tip
Primary = "I collected it". Secondary = "someone else collected it". If you did not observe, measure, count or ask it yourself, it is secondary.
Practice
Remember
Further reading
Books and resources for this unit
Sources and credits
The lesson text, rain-gauge diagram, tables, worked example and practice are written by Ganzaa. Census figures are from the National Institute of Statistics of Rwanda (2022 census).
