You are talking about a vehicle that would have to carry dozens if not hundreds of terabytes of data. The boot would literally have to be filled with hard drives. If you are in the US you should be able to tell it to drive from one coast to the other, or if you are in Europe the car should be able to drive from Warsaw, Poland, to Aberdeen, Scotland. And what do you mean only local data needs to be updated? Why? Updating a "dumb" TomTom map takes hundreds of megabytes a month just for one country, and we are talking about much more complex data, not just a 2D map.
The car could have some sort of wireless (4G, WiFi, etc...) to download updated/detailed data for new routes when it needs it, and store locally what it will likely need again in the future. Since the car knows where it's going, as long as it has some idea of when it will be in range of a wireless access point, it can plan when and how it will download the rest of the trip information on the way.
As long as the car has basic route information and knowledge about where it will be able to connect to servers with updated information. Cars could drive anywhere with basic road info, and download updated and more detailed information (intersection metadata, possible closures, etc...) only as needed. It doesn't always need to be in wireless range, it just needs to know when it will be so it can plan accordingly.
It needs one large read-only copy of data, plus one hard drive with updates. Those updates are limited to say a 1000 mile range (most people don't travel 100 miles from home in a month; in any case most people travel the same routes)
Sure, but if we want automatic cars to eventually replace manual cars we need to make sure they cover 100% use cases, not just most of them. Some people drive 10 miles to work and back, some people do 1000 miles a week driving through multiple countries. You need to deal with both, because nothing is stopping me from hopping in my car right this second and driving across the continent if I wish to do so. I wouldn't want an automatic car to hinder that freedom either.
