Grand theft auto - Map Waypoint

Does anyone know how, I would go about making a map, and then added a something that let you add waypoint to it, plus it would need to draw a line to it, and in game maybe arrow come up on the road, like saint row, or sleeping dog.

The professional way would be - as I learned in my studies, to implement a Dijkstra algorithm (Dijkstra's algorithm - Wikipedia ). So you would define waypoints and connect them to each other and, using the algorithm, find the shortest route.

To make the map itsself there are a lot of examples you can use. Google “unity3d minimap” for example.