As I highlight an area of a country with leafletjs the only way I have seen is using a Geojson file I used mapzen and it works but there is another way of doing it this way the problem that I have is that the geojson files weigh heavily (up to 15mg) and I am worried about the performance of the application, in the application that I am doing it is on a map of my country, they are 18 departments
Here's an example, that's what I'm looking for link