Select Point Data inside Geographical Boundary

Here is an example on how to select point data inside the geographical boundary by using point inside polygon function.

(* all the cities {name, coordinates} in Indiana *)
allcities = {First[#], CityData[#, "Coordinates"]} & /@ CityData[{All, "Indiana", "UnitedStates"}];

We like to select the cities inside St. Joseph county.
Boundary of St. Joseph county is imported as Polygon. See details on importing GIS data.

In Mahtematica-users Wiki, there is an discussion on Point Inside Polygon. We choose the first solution, since it works on non-convex polygon.

(* select cities by Point inside Polygon function *)
Select[allcities, PLSPolygon[countyboundary, #[[2]]] &]