A few people have been asking how to make something similar. The secret of the implementation seems to be solved. The map is fullscreen all the time. Only the sidebar is swithed on and off over the map.
Copying the idea is not very simple. There are many tricky details to be solved. Most of them are solved now. See the page.
The base and basic components for better map pages are about constructed. A page that imports and parses its data from text files, puts it on map and in collapsible interactive sidebar with category switching.
Now we can concentrate more at filtering the data and fine tuning the actual map UI.