Missing .prj files? about historical-world-atlas HOT 3 OPEN

I think the shapes there should be unprojected. Not sure why they are not properly projected by Mapbox. But you could try to load the shapes in QGIS and reproject them to any projection, then maybe also export with a .prj file

from historical-world-atlas.

Thanks @ilyabo for your prompt reply. So which projection should I use?

from historical-world-atlas.

This is a late answer, but it depends what you're showing and why. (I'm speaking in general terms; I don't actually know what MapBox supports.)

If you just want to display the continental US, you probably want to use the Albers Equal-Area conic projection, which is what most modern US governmental departments use. Canada only? Lambert conformal conic projection. (Other northern and southern countries will similarly benefit from conic projections.)

This is a great guide from CUNY that we've used at my workplace:
http://www.geo.hunter.cuny.edu/~jochen/gtech201/lectures/lec6concepts/map%20coordinate%20systems/how%20to%20choose%20a%20projection.htm

If you're visualizing dots on the full globe, note what it says under "Why equal-area projections are essential for dot-density maps?"

from historical-world-atlas.