We're building a project that lets you visualise data about zones within cities such crime rates and wealth. So for example in London you could compare the various boroughs. For this, I need to bulk download shapes (preferably geoJSON) that outline the zones within cities. For example, https://github.com/utisz/compound-cities contains such data for 3 cities (New York, London & Tokyo).
I have found this data provided by the city governments on their individual sites, but at the world scale that we'd like to approach, it isn't practical to go looking for each city separately. Is there any unified data source for each country or even for the world where we could get shape data for zones within cities? Perhaps an API for a mapping tool or GIS database?