This paper discusses how to establish multilayer storage structure and automatically reduce small scale graph from large scale mapping database by theory of changed-focuses Datum Model.
作者通过变焦数据模型原理，探讨如何建立多层存贮结构，将数字地图中的大比例尺地图数据库自动导出小比例尺图形。
It also discusses the theory about it, and puts forward three steps such as source data description, data structure mapping and data recombination.
对数字地图出版中多源矢量数据利用理论进行了探讨和研究，提出了源数据描述、数据结构映射和数据重组的解决方案。
The structure and working theory of data mapping tier is explained, and the method can improve the specialization of programming, reusability and maintainability of code.
结合项目实际，说明了它的结构和工作原理，该法提高了编程工作的专业化水平和代码的可重用性，增加了可维护性。
The structure and working theory of data mapping tier is explained, and the method can improve the specialization of programming, reusability and maintainability of code.
结合项目实际，说明了它的结构和工作原理，该法提高了编程工作的专业化水平和代码的可重用性，增加了可维护性。
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