Urbanisation

4. High level of this gas in cities, often from cars and factories (10 letters)
5. One effect of urbanisation, with crowded housing and lack of space (11 letters)
7. Natural areas within cities meant for public enjoyment (5 letters)
9. Form of housing built quickly and cheaply, often unsafe (8 letters)
10. Unplanned and often illegal settlements, typically on the outskirts of a city (10 letters)
12. Large retail spaces on city outskirts that encourage suburban shopping (9 letters)
15. Type of development where cities spread outwards, often creating suburbs (10 letters
17. Rising cost of living in urban areas due to demand (10 letters)
19. Movement of people from rural areas to cities (13 letters)
20. Tightly packed buildings without adequate public spaces, often in cities (7 letters)
21. Process by which an area becomes more industrial (14 letters)

1. Transportation that serves the public, like buses or subways (11 letters)
2. Jobs or industries in a city that involve services rather than goods production (9 letters)
3. Large city with significant political or economic influence (8 letters)
6. Type of area where population density is low and land is mostly agricultural (5 letters)
8. Type of pollution caused by city lights at night (10 letters)
11. Type of pollution associated with noise in urban areas (5 letters)
13. The opposite of urban areas; often agricultura
14. High-density residential buildings in urban areas (9 letters)
16. City area known for residential living and local amenities (8 letters)
17. New or improved area in a city, often to attract higher-income residents (13 letters)
18. Area of a city where commerce and business activities are concentrated (3 letters)