Maybe high Technology should increase urban population density somewhat? I’m guessing this because of how high tech industries tend to concentrate in certain cities and attract people to move to those cities.
What would be really interesting would be policies designed specifically to increase/reduce UPD. Some ideas could include:
Urban Development Tax Breaks: through tax breaks for high-density urban development, more buildings are built in cities. This would increase UPD and the GDP somewhat, as well as private housing.
City Council Subsidies
The government subsidises the local governments of major cities in order to let them function more effectively. This increases urbanisation and approval from Socialists, and upsets Capitalists slightly.
Limit Co-living
The government places regulations on two or more unrelated people sharing a home and both contributing to its rent, this reduces Urban Population Density significantly and upsets Poor, Liberals and Youth. This sounds crazy but it has happened in a city level.
You could also use some ideas from this guy though de-urbanisation is not necessarily a good thing, he has some ideas you could use.