Nearest capital in Europe

For those who don’t know already, this is called a Voronoi diagram.

I think I'm too stupid to understand this. How are they straight lines and not at a diameter / in a circle from any given point? It seems... wrong.
- Does this animation help?
  
  https://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/Voronoi_growth_euclidean.gif/440px-Voronoi_growth_euclidean.gif
- What does the separating line between two circles look like?

I, for one, support the Republic of Great Ireland and Northern Britain

On this map, you can see why Denmark's capital is Copenhagen. When Denmark controlled Scania and Schleswig-Holstein, it was much more centrally located than today. The borders of Denmark in this map correspond roughly to the borders before the Treaty of Roskilde.

it's also weirdly accurate to where people might commute to copenhagen today
Make Scania Danish Again
- Seconded, if Danes would take the hot potato out of their mouth and start speaking proper Swedish. :p

I think that these should not be straight lines regarding that the Earth is a sphere. Especially between Moscow and Helsinki.

https://math.univ-lyon1.fr/~alachal/diaporamas/diaporama_cartographie3/Great_Circles.htm
it should also take into account transport feasability to at least some degree, like no one in their right mind would associate narvik with helsinki..
- For railway, there is already some neat project for visualising the reach in a certain travel time from any city with a station. https://www.chronotrains.com/de/explore

this i an amazingly informative rendering.

What about Edin, bruh?

As a finn, I approve these new borders.

Suur-Suomi !

I’d much rather be ruled by my closest capital.

~~North~~ Macedonia

There's something funky going on north of valleta

How did u make this

I don't know how NaytaData made it, but if I were doing it, I would do something like this:

start with a "blank" un-coloured map of coastline and country borders

put all the "capital" cities on the map

make a temporary grid of points over the map and find the closest city for each point

paint the map based on those temporary grid points

I would use a computer but the same steps would work with paper & pen.
- If the OP is using GIS, it can be even easier.
  
  Your first two steps are spot on, but then step three could simply be to add a large buffer for each capital and use some and/or/nor/xor (I'd have to look up to be certain) rules to have the buffer zones not overlap, but end where touching. Apply a color scheme and you're in business.

Voronoistan Union

Superb way to illustrate.

Where’s Edinburgh?

Scotland is part of the UK sadly
- Scotland is one of the four countries comprising The United Kingdom of Great Britain and Northern Ireland. The others are England, Wales and Northern Ireland. Scotland’s capital is Edinburgh.