I looked up Sunderland Street, Tickhill, England on the new Maps app, and all the streets shown in the old Maps screenshot in the second image are there. Perhaps they've already added the missing data? The Satellite imagery in that area remains particularly bad, though. I think if Apple can iterate and improve the app quickly, the initial errors won't be that significant.
My best guess is there's a problem in serving the map data up to users.
Vector slippy maps run on bounding box searches - if I look at New York, my client says to the server "Tell me all the roads within this square" with the latitude and longitude of wherever I'm looking.
There's a lot of data - too much to store on one server - and the data doesn't all shard naturally. You can divide the world up into squares and store different squares on different servers, but long roads cross many squares, big objects like country borders belong in many squares, and when you're zoomed out your view covers many squares.
The server also has to be clever; I don't actually want every road in New York or the data would take forever to load. I only want the major roads when I'm zoomed out.
All these problems are solvable - spatial databases like PostGIS have been able to perform bounding box queries for years - but I don't know of anyone using PostGIS to support the millions of users Google have. It's well known that for regular data Google has things like BigTable, fancy NoSQL stuff that's supposed to scale well; I assume they have a geospatial database along similar lines. It's possible Apple decided to develop something similar.
My guess as to how [1] came about is that the user started zoomed out, so they only got sent major roads, then when they zoomed in some hiccup prevented loading the minor roads. This could have been as simple as the user's wifi going down, or it could that Apple's database servers are overloaded or have bugs.
I have been using 6 since the first beta versions and one thing I have noticed is sometimes they show up, sometimes they are misplaced and sometimes they are not even there. My rough guess that this may have something to do with the accuracy of your location seed, and the algorithm they use to place stuff around where they think you are. I would imagine they factor it in for error correction and maybe when they get a less accurate seed, it throws everything off. It's a wild guess but based on my limited observation it seems like something like that is happening, some times it nails it and sometimes you get a WTF. I usually just do another search and it clears it up, but that only works if you know what you are looking for, which is my general use case for maps.
