==liên kết ngoài==* nps official website* nps research links/reference desk* nps library information center* nps focus digital library & research station* nps historic photograph collection* nps broll video (public domain)* nps digital image archives (public domain)* nps civil war soldiers and sailors system (cwss)* community assistance available from the national park service* criteria for inclusion in the national park system* designation of national park system units (national monument vs national park etc)