My own project (https://plantogether.city) hopes to help make cities better from an urban planning perspective by enabling two things:

1. Giving people a voice. People don't feel a sense of belonging because they a single individual amongst thousands/millions. Being able to discuss things directly on a map with other citizens is empowering.

2. Serving as a spatial knowledge base. Allows users to collaboratively catalog the best, worst, most interesting etc. parts and elements. For example all items tagged with cycling in Waterloo (https://plantogether.city/tag/cycling?area_id=3).

Having more organized information and discussions could go a long way in improving decision making.