Reading: Diagram & Flow Chart Labeling

Real-world analogy

What is it?

Diagram Labeling and Flow Chart Completion are visual IELTS Reading question types. You receive a visual representation — a diagram, illustration, map, or flow chart — related to the passage, with some labels missing. Your task is to complete the missing labels using words from the passage. These questions test your ability to connect written descriptions with visual representations.

Real-world relevance

Reading a diagram alongside a text is a core academic skill. Medical students read anatomy textbooks with labeled diagrams. Engineers match technical specifications to blueprints. Even cooking involves following a recipe (text) while looking at step-by-step photos (visuals). IELTS tests this because it is essential for university study.

Key points

• Diagram Labeling Format — You receive a diagram, illustration, or technical drawing related to the passage with blank labels. You must fill in these labels using words from the passage (within a word limit) or select from a list of options. Diagrams can show machines, buildings, scientific processes, geographical features, or biological structures.
• Flow Chart Format — A flow chart shows a sequence of steps or stages in a process. You must complete the missing labels in the correct order. Flow charts follow a linear or branching path with arrows showing direction. The key is understanding the SEQUENCE — what happens first, second, third, and so on.
• Orientation First — Before reading any labels or gaps, spend 30 seconds studying the diagram or flow chart. Understand what it represents. Identify the starting point, the direction of flow, and any labeled parts that are already provided. These given labels are your anchors — use them to locate the relevant section of the passage.
• Use Given Labels as Anchors — Pre-filled labels on the diagram are your best friends. They tell you exactly which part of the passage to read. If the diagram already shows "evaporation" at step 1, scan the passage for "evaporation" and read the surrounding sentences to find what comes before and after it.
• Passage Sequence Matches Diagram — The description in the passage typically follows the same order as the diagram — top to bottom, left to right, or start to finish. Once you find where the process starts in the passage, read through it linearly and fill in the diagram labels in order. Do not jump around.
• Technical Vocabulary — Diagram questions often appear in passages about science, technology, or industrial processes. You may encounter unfamiliar terms like "centrifuge," "filtration," or "condenser." Do not panic — you do not need to understand the science. Just match the passage descriptions to the diagram positions.
• Map Labeling Variant — Sometimes the diagram is a map showing locations of buildings, rooms, or geographical features. You must label places on the map using information from the passage. Direction words like "north of," "adjacent to," "opposite," and "between" are critical clues. Trace the route described in the passage on the map.
• Word Limit Vigilance — As with Sentence Completion, diagram and flow chart labels have strict word limits. A label of "the water filtration system" (4 words) would be wrong if the limit is "NO MORE THAN TWO WORDS." Check whether articles like "the" or "a" are necessary — usually they are not in labels.
• Common Mistakes — Students often make three errors: (1) writing labels in the wrong position because they misread the arrow direction, (2) exceeding the word limit by including unnecessary articles or adjectives, and (3) guessing based on the diagram rather than checking the passage. Always verify your answer against the passage text.

Code example

PASSAGE:

The Water Purification Process

Raw water from rivers or reservoirs first passes through
a coarse screen to remove large debris such as branches,
leaves, and plastic waste. The screened water then enters
a sedimentation tank, where it is held still for several
hours, allowing heavy particles like sand and silt to
settle to the bottom by gravity.

After sedimentation, the water undergoes coagulation.
Chemicals called coagulants — typically aluminium sulfate
— are added to the water. These chemicals cause tiny
suspended particles to clump together into larger masses
called flocs. The flocs are then removed in a flotation
tank, where air bubbles carry them to the surface for
collection.

The water next passes through a series of sand filters.
These multi-layered filters contain gravel at the bottom,
coarse sand in the middle, and fine sand on top. As water
moves downward through these layers, remaining particles
as small as 0.5 micrometres are trapped.

Finally, chlorine is added in a process called
disinfection to kill harmful bacteria and viruses. The
treated water is stored in covered service reservoirs
before distribution to homes through underground pipes.

FLOW CHART COMPLETION (No more than TWO WORDS):

[Raw Water]
     |
     v
[1. ________] --> removes branches, leaves, plastic
     |
     v
[2. ________] --> heavy particles settle by gravity
     |
     v
[Coagulation] --> aluminium sulfate added
     |
     v
[3. ________] --> air bubbles remove flocs
     |
     v
[4. ________] --> traps particles down to 0.5 micrometres
     |
     v
[Disinfection] --> chlorine kills bacteria
     |
     v
[5. ________] --> water stored before distribution

ANSWERS:
1. coarse screen (from "passes through a coarse screen")
2. sedimentation tank (from "enters a sedimentation tank")
3. flotation tank (from "removed in a flotation tank")
4. sand filters (from "passes through a series of sand
   filters" — "series of" is not needed for the label)
5. service reservoirs (from "stored in covered service
   reservoirs" — "covered" is extra detail not needed)

Line-by-line walkthrough

1. 1. The passage describes water purification in sequential order: screening, sedimentation, coagulation, flotation, filtration, disinfection, storage.
2. 2. The flow chart has the same sequence. Pre-filled labels "Coagulation" and "Disinfection" are anchors — they help us know exactly where we are in the passage.
3. 3. For blank 1, the description "removes branches, leaves, plastic" matches paragraph 1: "coarse screen to remove large debris such as branches, leaves, and plastic waste." Answer: "coarse screen."
4. 4. For blank 2, "heavy particles settle by gravity" matches "sedimentation tank, where... heavy particles like sand and silt settle to the bottom by gravity." Answer: "sedimentation tank."
5. 5. For blank 3, "air bubbles remove flocs" matches "flotation tank, where air bubbles carry them to the surface." Answer: "flotation tank."
6. 6. For blank 4, "traps particles down to 0.5 micrometres" matches "sand filters... remaining particles as small as 0.5 micrometres are trapped." Answer: "sand filters."
7. 7. For blank 5, "water stored before distribution" matches "stored in covered service reservoirs before distribution." We write "service reservoirs" — omitting "covered" to stay within the word limit and because it is a modifier, not the core label.

Spot the bug

A student completed the flow chart like this:

1. "screen" (instead of "coarse screen")
2. "sedimentation" (instead of "sedimentation tank")
3. "floc removal" (instead of "flotation tank")
4. "gravel and sand" (instead of "sand filters")
5. "underground pipes" (instead of "service reservoirs")

Explain like I'm 5

Fun fact

Hands-on challenge

More resources

• IELTS Reading: Diagram Labeling Tips (IELTS Liz)
• IELTS Academic Reading Practice (British Council)
• Flow Chart Completion Strategies (IELTS.org)
• Cambridge IELTS 15 Academic - Reading Tests (Cambridge)