'Like with like' in Task 1

The population of Japan is lower than Thailand.

This is an example of not comparing like with like.

In the noun phrase 'the population of Japan', population is the main noun. Population, which is a mass of people, is said here to be lower than Thailand, which is a land mass.

This leaves the reader with an image of Thailand hovering up in the air, with the Japanese population some physical distance below it!

A mass of people is not like a land mass. In order to make sure that you're comparing like with like, use a parallel structure:

The population of Japan is lower than the population of Thailand.

This may result in some repetition - 'the population of' is used twice. But don't worry about repetition. Just make sure that you're comparing like with like.

Avoiding repetition - uncountable and singular nouns

If you want to avoid repeating a noun that is either uncountable or singular, you can use that as a substitute:

The population of Japan is lower than that of Thailand.

In this example, that replaces the population.

Avoiding repetition - plural nouns

If you want to avoid repeating a noun that is plural countable, you can use those as a substitute:

Prices at traditional markets are lower than those at supermarkets.

In this example, those replaces prices.