Cyberpunk 2077 directory, Richard Borzymowski, has confirmed that the map in Cyberpunk 2077 will be a "little smaller" than the map size in The Witcher 3, but promises this will be made up for by being "far denser", in an interview with GamesRadar this past week.
This does not mean that the map will be small by any means, The Witcher 3's map was huge, but given the difference in the two settings, it makes sense, really. The Witcher 3 was mostly natural landscape, relatively easy to create and render compared to huge cities. Speaking of the differences, Borzymowski said;
If you look at pure surface square kilometres, then Cyberpunk 2077 might even be a little bit smaller than The Witcher 3, but it’s the density of the content, taking the world of The Witcher and squeezing it right in, deleting the wilderness between. Obviously...in The Witcher we were an open world with vast lanes and forests in between smaller cities and larger cities like Novigrad, but in Cyberpunk 2077 we’re set in Night City, it’s an integral part of the setting; it’s essentially a protagonist if you want to call it that, so it has to be denser. It wouldn't give us the end effect we wanted to achieve if the city wouldn't be believable...so we packed it full of life."
The city in Cyberpunk 2077 will split into six different districts, and the player will be able to travel throughout the entire map seamlessly with no loading screens. CD Projekt Red will be talking more about the various districts soon when the 15 minute gameplay livestream takes place next week, so stay tuned to GameFront for more on this as we learn it.