Polygons can be quite complicated.

GeoJSON allows for an easy way to describe polygons with (multiple) interior gaps.

  • Polgyon
    • LinearRing (exterior)
      • Positions
    • LinearRing (interior)
      • Positions
    • LinearRing (interior)
      • Positions

Only 1 exterior ring and then as many interior rings as needed

{ "type": "Polygon",
	"coordinates": [
			[[35,10], [45,45], [15,40], [10,20],[35,10]],
			[[20,30], [35,35], [30,20], [20,30]]
		]
}

Care also should be taken with coordinate ordering in GeoJSON Polygons

The exterior ring should be counterclockwise
Interior rings should be clockwise

Why does this matter?

The classic Chamberlain & Duquette algorithm for calculating the area of a polygon on a sphere has the nice property that counterclockwise-wound polygons have positive area and clockwise yield negative. If you ensure winding order, calculating the area of a polygon with holes is as simple as adding the areas of all rings.
Winding order also has a default meaning in Canvas and other drawing APIs: drawing a path with counterclockwise order within one with clockwise order will cut it out of the filled image.

source: More than you ever wanted to know about geojson