Displaying regional borders on a map is a common practice. Here's how to obtain borderline area in GeoJSON format.
- Download regional borders
There is often a plethora of geographic boundary data available in GeoJSON format on the internet. However, not all regions may have GeoJSON data. Therefore, one possible approach is to search for area boundary data in shapefile format.
There are two website you can visit:

This website is required users to have account first.
Changing the format data from shapefile to geoJSON data using this website.

After converting, data ready to use.
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