Actually, to my knowledge, there are three zones. The Combat Zone, a zone that was utterly abandoned by the police and all forms of governing, who follows no rules but the ones set by the gangs that have taken over. These are the slums.
Then there is a standard like zone whose name escapes me at the moment. This zone is full of the people that work for the major corporations that run the world of CyberPunk. Though these people are mostly destitute, there is still law enforcement and order in this zone. I'm assuming that this is the zone showcased in the Teaser Trailer.
Finally there is the Corporate Zone full of the hotshots CEO's and managers of the corporations that have taken over. I guess this would be the downtown zone. Not sure if there is much danger here, I mean there has to be but not like in the other zones.
There aactually many many districts i Night City...
This is the map from the Night City Sourcebook, one of the most detailed indepth rpg sourcebooks of its kind for any rpg.
That's only the upper half of the map presented in the core rule book, which any way you look at it, is a small section of city. And even in the above map, there is Corporate Plaza, a City Center, a Little Italy, a Japan Town, A China Town, a University District, shopping areas, Warehouse areas,a stadium, a large park,. Do you know what doesn't appear anywhere on this map? The Combat Zone. None of the areas on this map are actually slums... some are better than others, others are worse... but nothing is the combat zone.
And like I said, this is just a small section of the city.... and certainly doesn't take into account the suburbs and outlying areas.... nor does it take into account the areas outside the core city.such.
Even my own ridiculously sized map of Night City, made by cutting and pasting together bits of cities from all over the US, only covers the city proper, and doesn't cover the the industrial section to the south, the upper class suburbs on the other side of the bay, or the Nomad Market to the west. (Granted my map isn't canon by any means, but it shows the scope and size of the city.... not that I in any way believe CDPR, or any game company would be able to pull off something that size).
On my map, the darker area in the upper right hand corner is the german version of the same night city map that is present in the core books. Just to give a sense of scale to everything.