Point in complex shape

[Jimmy Eriksson]

Im probably missing out on something here, but how can I check if a point is within a shape that is not just a simple fourcornered box?
What I would like to do is to check if a point is within the borders of a country. My plan is to somehow create a geometrical shape from rough points that simplifies the shape of the country, but this of course cannot be simplified to only four points so a simple polygon won't do. Ideas anyone?

Thanks in advance

//Jimmy