Calculate the distance between two points in bing cards

See Haversine or even better Vincenty how to solve this problem.

The following code uses the haversines method to obtain the distance:

public double GetDistanceBetweenPoints(double lat1, double long1, double lat2, double long2)
    {
        double distance = 0;

        double dLat = (lat2 - lat1) / 180* Math.PI;
        double dLong = (long2 - long1) / 180 * Math.PI;

        double a = Math.Sin(dLat / 2) * Math.Sin(dLat / 2)
                    + Math.Cos(lat1 / 180* Math.PI) * Math.Cos(lat2 / 180* Math.PI) 
                    * Math.Sin(dLong/2) * Math.Sin(dLong/2);
        double c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));

        //Calculate radius of earth
        // For this you can assume any of the two points.
        double radiusE = 6378135; // Equatorial radius, in metres
        double radiusP = 6356750; // Polar Radius

        //Numerator part of function
        double nr = Math.Pow(radiusE * radiusP * Math.Cos(lat1 / 180 * Math.PI), 2);
        //Denominator part of the function
        double dr = Math.Pow(radiusE * Math.Cos(lat1 / 180 * Math.PI), 2)
                        + Math.Pow(radiusP * Math.Sin(lat1 / 180 * Math.PI), 2);
        double radius = Math.Sqrt(nr / dr);

        //Calculate distance in meters.
        distance = radius * c;
        return distance; // distance in meters
    }

You can find a good site with information here .