관련 내용들이 많이 있네요 참고하세요
http://dkdlel072.tistory.com/entry/%EC%95%88%EB%93%9C%EB%A1%9C%EC%9D%B4%EB%93%9C-%EA%B0%81-%EB%8B%A8%EB%A7%90%EA%B8%B0%EC%9D%98-%ED%95%B4%EC%83%81%EB%8F%84%EC%99%80-Drawable-%EC%9D%B4%EB%AF%B8%EC%A7%80%EC%9D%98-%EA%B4%80%EA%B3%84-dpi
http://developer.android.com/intl/ko/design/style/devices-displays.html
http://nuninaya.tistory.com/583
http://blog.acronym.co.kr/188