What is the best program for drawing large maps?
So I have a layout and a sketch for a map that I've been working with for years but I want a way to draw it in high resolution with the ability to zoom in and still view small details and text at least semi clearly. Most art apps I've used are alright but the details get quite fuzzy upon zooming in and text especially basically becomes unreadable. But I've seen lots of world maps drawn by people and posted on here that are fairly crisp and easy to read. So what are the best methods for creating a detailed map digitally?
A good example of what I'm looking for is this speculative map of the world of Game of Thrones. While not perfect, you are able to fairly easily explore small details and read the text without much trouble (if you download the file that is) https://www.reddit.com/r/gameofthrones/s/ud0xJo0XCn
Does anyone know how this was done or what I can do to achieve similar results?