1. Draw a big circle on paper or computer to represent the whole mathematics in Unit 4.

2. Four lines extend from the great circle, and a small circle is drawn at the end of each line, which respectively represents the four main contents of "comparison length", "comparison size", "thousands of dozen" and "writing formula".

3. Write down related keywords or phrases next to each small circle, such as "length" and "size" next to the "shorter" circle, which can clearly show the focus of each topic.

4. Draw more lines along each small circle, and draw a few small circles at each end to represent more specific sub-themes (for example, there may be sub-themes such as "Measure the length with a ruler" and "Compare the length directly" under "Length").

5. Write down relevant keywords or phrases beside the subtitle to better summarize the key content of the subtitle.

6. Finally, you can further polish and beautify the mind map, such as adding colors or backgrounds.

Knowledge points of fourth grade mathematics

1 ton =1×1000 =1000 kg; 1 kg =1present1000 = 0.001ton

1kg = 1× 1000 = 1000g； 1g = 1÷ 1000 = 0.00 1kg

Length:1km =1×1000 =1000 m; 1 m =1÷1000 = 0.001km

1 decimeter =1×10 =10cm; 1 cm =1present10 = 0.1decimeter

1cm = 1× 10 = 10mm； 1 mm =1present10 = 0.1cm

1 decimeter =1×100 =100 mm; 1 mm =1÷100 = 0.01decimeter

1 m = 10 decimeter =100 cm =1000 mm; 1 mm =0. 1 cm =0.0 1 decimeter =0.00 1 meter

Area: 1 m2 =/kloc-0 /×100 =100 square decimeter; 1 square decimeter =1÷100 = 0.01square meter.

1 square decimeter =1×100 =100 square centimeter; 1 cm2 =1÷100 = 0.01square decimeter.