A subway is very different from an intercity railway network. For one, there's probably fewer different routes on the subway so trains conflict with each other less. Also, a subway doesn't have to accomodate freight traffic as well.

> there's probably fewer different routes on the subway so trains conflict with each other less

This isn't obvious to me. Here's Deutsche Bahn's map of the system: https://cms.static-bahn.de/wmedia/redaktion/aushaenge/streck...

Here's a map of Shanghai's subway system: https://www.travelchinaguide.com/images/map/shanghai/subway-...

The German intercity rail network certainly identifies more lines, around 57 to Shanghai's 18, but this isn't directly related to the complexity of the topology. For example, line 14 appears to begin in Aachen and dead-end into Berlin, at which point line 95 begins in Berlin and runs out to Poland. As far as the routing is concerned, those could be the same line. But they're given different numbers. When the same thing happens (at a smaller scale) in Shanghai at the west end of line 9, the tail bit of the line going to Songjiang is still called "line 9". Note that if you want to ride out to Songjiang, at some point you're going to have to get off your "line 9" train and walk over to another station where a different "line 9" train will take you the rest of the way.

Discounting that, the two layouts appear to be roughly similar on the fundamentals, if differently scaled.

The most obvious difference is that the routes between major German cities are served by several lines. This is clearly meaningful in some cases; line 29 from Munich to Nuremberg continues north to Hamburg via Berlin while line 41 from Munich to Nuremberg continues northwest to Dortmund via Frankfurt and Cologne. On the other hand, line 8 from Munich to Nuremberg parallels line 29 for the entire length of line 8 (line 8 stops in Berlin, but line 29 doesn't).

My first guess would be that conflicts arise from the fact that the German trains are on the ground, and when their tracks cross, conflict can occur. This isn't true of a subway system; when subway tracks cross, they do it at different altitudes, allowing both tracks to be in use simultaneously.

Not only do tracks cross, trains also share tracks and platforms. In Shanghai only Line 3 and 4 share tracks and platforms.

Your map only shows ICE/IC lines, there are many more other lines which share the same tracks. This shows a more complete picture: https://www.deviantart.com/costamiri/art/Transit-diagram-of-... but it still doesn't show international trains and freight.

Im talking about trains between cities. Frankfurt is 190km from Cologne for instance.

Trains inside cities (i.e. trams and subways) are much much more frequent because they have fewer constraints and lower speeds.

How does that affect the question of whether the network is densely packed or whether it has frequent trains?

Passenger trains from Frankfurt to Cologne are infrequent because there is virtually no demand to move between cities 120 miles apart. Because the trains are infrequent, they aren't dense on the tracks.

But that's the opposite of saying that they are frequent and densely packed.

Read up on what affects railway bandwidth. A densely packed 250km/h line won't appear similar to a densely packed subway line to a bystander despite of maxing out its abilities.

Connecting train doesn't mean that it runs on the same tracks. The train stations where you would switch tend to have ~6 to ~20 different platforms.