Maps are composed of symbols, the geographic features that were mapped will hold the geometric correlation with those symbols. In the process of map production, map data gathering means to sampling from these features. The density and frequency of data sampling will went higher when the map scale became more larger, and the spend of mapping will increasing quickly. The theme of this article is to discuss the definition and essence of the base map. Besides, the influences of scale factor in the constituting of national base map series were also be considered. It is helpful in the development of national mapping.