Free Shapefile maps are easier to obtain than GeoJSON maps. Fortunately, it is easy to convert Shapefile maps to GeoJSON.
Subscribers of StatPlanet Cloud have access to over 450 national and regional maps optimized for the web, in GeoJSON format.
Optimizing your maps for the web
GeoJSON maps tend to be lightweight and are the preferred format for the web. However, shapefile maps can also be optimized using free tools. Often they can be reduced in size by as much as 90% with no significant changes in map appearance at normal zoom levels.