Fig. 1 is a proportional-symbol map prepared for a global energy study. Each circle represents annual electricity generated from renewable energy in selecte...
Question 1 Report
Fig. 1 is a proportional-symbol map prepared for a global energy study. Each circle represents annual electricity generated from renewable energy in selected cities in 2020. The largest circle is for Shanghai, China. The map is intended to help students compare the scale of renewable energy generation between cities, rather than to show every source of energy consumed by each city. The researcher used a circle key, because the area of each circle, not its diameter, should be proportional to the value represented. Students must use the figure carefully when making calculations and drawing conclusions.
(a) Identify the city with the greatest renewable electricity generation. [1]
(b) Identify the difference in generation between Shanghai and Berlin. Show your working. [2]
(c) Identify the total generation shown for the two African cities. Show your working. [2]
(d) Identify two advantages of a proportional-symbol map for presenting these data. [4]
(e) Identify two limitations of comparing circle sizes by eye in Fig. 1. [4]
(f) Identify two factors, other than renewable generation, that should be considered before judging which city has the most sustainable energy system. [4]
(g) Identify one conclusion and one caution about global comparisons based on this small selection of cities. [3]
Answer Details
(a) Shanghai has the greatest renewable generation, shown as 260 TWh. [1]
(b) \[260\text{ TWh}-135\text{ TWh}=125\text{ TWh}\] The difference between Shanghai and Berlin is 125 TWh. [2]
(c) The two African cities are Cairo and Cape Town:
\[25\text{ TWh}+60\text{ TWh}=85\text{ TWh}\]
The total is 85 TWh. [2]
(d) Advantages of a proportional-symbol map include that it:
- shows each city's location;
- shows the spatial pattern of values;
- makes larger values stand out visually;
- allows several cities to be compared in a global geographical context.
[4]
(e) Comparing circles by eye is limited because:
- the area of a circle is harder to judge accurately than its diameter;
- circles can overlap and obscure places;
- exact values require labels or the key;
- very small values may be difficult to see.
Map scale or projection can also affect apparent spacing. [4]
(f) Renewable generation alone does not show the sustainability of an energy system. Consider:
- total energy consumption and population, so per-capita generation can be considered;
- the extent of fossil-fuel use and emissions;
- energy efficiency and reliability of supply;
- energy used by transport.
[4]
(g) A valid conclusion is that Shanghai has the highest value in this figure. However, only four cities are shown, and these are total values that do not account for population or total consumption. Therefore the figure cannot rank all cities globally by energy sustainability. [3]
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