Given a list of GPS coordinates making up a boundary, how can I calculate if my location is within that boundary?

Question

Suppose I have hundreds, or even thousands of GPS coords, Latitude and Longitude that make up a boundary around a country.

I also have my current position Latitude and Longitude.

How can I determine (using C#, programming for Windows10 UWP) if my position is within the boundary of a country?

E.G. Suppose I have all the points that make up red line in the image below. If I was at the X location, my function would return true. If I were at the Y location, my function would return false.

Answer 1

Thanks to the two answers received I found out the actual name of what I was trying to do... "Point in Polygon".

Knowing this, I was able to find this Stack Overflow question and answer

Here's the code should the above ever disappear:

/// <summary>
/// Determines if the given point is inside the polygon
/// </summary>
/// <param name="polygon">the vertices of polygon</param>
/// <param name="testPoint">the given point</param>
/// <returns>true if the point is inside the polygon; otherwise, false</returns>
public static bool IsPointInPolygon4(PointF[] polygon, PointF testPoint)
{
    bool result = false;
    int j = polygon.Count() - 1;
    for (int i = 0; i < polygon.Count(); i++)
    {
        if (polygon[i].Y < testPoint.Y && polygon[j].Y >= testPoint.Y || polygon[j].Y < testPoint.Y && polygon[i].Y >= testPoint.Y)
        {
            if (polygon[i].X + (testPoint.Y - polygon[i].Y) / (polygon[j].Y - polygon[i].Y) * (polygon[j].X - polygon[i].X) < testPoint.X)
            {
                result = !result;
            }
        }
        j = i;
    }
    return result;
}

It takes an array of points that make up the polygon and a point to test and returns true or false. Works well in all my testing.