GitHub - ghuntley/geocoordinate: GeoCoordinate is a portable class library (in v1.1.x) or netstandard v1.1 (from v2.x.x) compatible implementation of System.Device.Location.GeoCoordinate. It is an exact 1:1 API compliant implementation and will be supported until MSFT sees it fit to embed the type. Which at that point this implementation will cease development/support and you will be able to simply remove this package and everything will still work.

PM> Install-Package GeoCoordinate

GeoCoordinate pin1 = new GeoCoordinate(lat, lng);
GeoCoordinate pin2 = new GeoCoordinate(lat, lng);

double distanceBetween = pin1.GetDistanceTo(pin2);