if i am not mistaken your answer is no you dont get any extra shields from outside your border you can get the resorce and share it with all your citys no matter how far as long as they are connected with a road or harbor but you only get shields for what is inside your boarder...
lets say you need horses and they are 6 moves away from your city you can move a worker to the horses then farm them and then build a road to connect your city and now you have horses
but you get no bonus for having them inside your boarders
on a side not eveytime i play this game i like to force myself on a island so i dont get attacked for atleast half the game