Here is an interesting set of maps (from this study) showing density trends, population trends, and residential area trends (i.e. sprawl), across Europe between 2006-2012 and 2012-2018:

The key takeaway is that, broadly speaking, there is -- or at least there was five years ago -- a new density trend across most European cities. From 2006 to 2012, the prevailing trend was de-densification. That is, fewer people per hectare. However, from 2012 to 2018, that trend largely reversed. With the exception of the Iberian Peninsula and Eastern Europe, the majority of cities flipped to densification.

The study tells us that there are two main reasons for this switch. The first is that more cities started growing again. During the first period, about 60% of cities in the sample size of 300+ cities, were adding people. In the second period, this figure increased to 75%. It's also worth noting that this growth is being largely driven by immigration, and increasingly so. The number of cities with positive natural growth diminished from 67% to 51% between the two study periods.

The second driver is a reduction in sprawl. Though almost every city in the study continued to expand outward, the rate of expansion was much lower between 2012 and 2018. So less land consumption, and more people. That's how you increase your urban density. Of course, it would be interesting to see if any of this has changed or reversed (again) as a result of the pandemic. 2018 kind of feels like eons ago, doesn't it?

This is a terrific set of maps published by The Washington Post (2015) using data originally collected and published by Peter Kerpedjiev:

What they show is how far you can travel in a 24 hour period using only trains and brisk walking from a collection of 28 European cities. In a few cases, such as from London to Dublin, a ferry ride is also included.

Here’s a zoom in on London:

The obvious takeaway is that Western Europe is very well connected, whereas many parts of Eastern Europe are not. Some cities, such as Tallinn (Estonia) and Podgorica (Montenegro) are almost completely disconnected.

Of course today there’s stiff competition from air travel.