Line graph
FoundationLines connect points, show trend.
- Line graphs show how data changes over time
- Three reading steps: check axes → read points → judge trend
- Calculate rises and falls by subtraction (28 − 22 = 6)
1Summary 重點摘要
Lines connect points, show trend.
2Vocabulary cards Vocabulary
A chart joining data points with lines, used to show trends over time.
The bottom line, usually time, e.g. 8am, 9am, 10am.
The side line showing the quantity, e.g. temperature (°C).
One plotted value, e.g. the point at 9am is 25°C.
The overall direction: rising, falling or flat.
The change between neighbouring points, e.g. 22 → 25 rises by 3.
How much each grid square stands for, e.g. 2°C per square.
The spacing on the time axis, e.g. one square per hour.
3Step by step Steps
- Step 1: Read the title and axesStart with the title, such as morning temperatures, to know what the graph shows. The horizontal axis is time (7am, 9am, 11am) and the vertical axis is temperature, 2°C per square. Titles and axes are the basis of every reading.
- Step 2: Read each pointFollow the line point by point: 7am = 22°C, 9am = 25°C, 11am = 28°C. Check each point against the vertical scale square by square instead of guessing, and note the values down for comparing later.
- Step 3: Find highest and lowestLocate the top point and the bottom point: highest 28°C at 11am, lowest 22°C at 7am, a difference of 28 − 22 = 6°C. Once these are found, the range of the data is clear.
- Step 4: Judge the trendLook at the line from left to right: 22, 25, 28 keeps going up, so the line slopes upward and the trend is rising. A downward slope means falling, and a flat stretch means no change. A trend describes the overall direction.
- Step 5: Compute a riseWork out how much one part rose: from 9am to 11am, 28 − 25 = 3°C in two hours. The steeper the line, the bigger the change in the same time, so that part rises faster.
- Step 6: Estimate between pointsFor times without a point, estimate sensibly: at 10am the line lies between 25 and 28, so about 26 to 27°C. Estimates must follow the line's direction between the neighbouring points, never a wild guess.
4Diagrams Diagrams
5Worked example Example
Example: a line graph shows morning temperatures: 8am 20°C, 10am 24°C, 12 noon 30°C. How much warmer is noon than 8am? What is the trend?
- Read the points: 8am = 20°C, 10am = 24°C, 12 noon = 30°C.
- Find the difference: 30 − 20 = 10, so noon is 10°C warmer than 8am.
- Judge the trend: 20, 24, 30 keeps rising, an upward trend.
- Compare the two rises: 8am to 10am rises 4°C; 10am to 12 noon rises 6°C.
- Conclusion: the later rise is faster and the line steeper, so warming speeds up towards noon.
- Answer: Noon is 10°C warmer than 8am, and the whole morning shows an upward trend that speeds up towards noon. We read the points first, then subtracted 30 − 20 = 10. Comparing the two legs, the first rises 4°C and the second 6°C, so the later line is steeper and the warming is accelerating.
6Common mistakes Mistakes
7Quick check Quick check
Q1What is a line graph best at showing?
Q2Line graph: 9am 22°C, 11am 28°C. What is the rise?
Q3In a falling trend, which way does the line slope?
Q4Each square is 5°C and a point sits 3.5 squares up. What is its value?
Q5Comparing votes across five subjects: line graph or bar chart?
8Recap Recap
- Line graphs show how data changes over time
- Three reading steps: check axes → read points → judge trend
- Calculate rises and falls by subtraction (28 − 22 = 6)
- Values between points can be sensibly estimated
- Comparing categories → bar chart; time trends → line graph