求翻译：地 图 上很难 一 一 表 示它 们 的 特性用 图 者，也不 一定需 要 了 解如 此 详 细 的特 征于 是就 出 现了 将 制 图 物体 进行 分 类，分级 的表 示 方法 即 用 抽象 的具有 共性 的 符号 来 描绘 某 一类 级 客 体对象 。例 如 用 两种不 同 颜 色 或晕 线符 号 区 分 建筑物 的 坚 固 与不 坚 固 的特征 用 几 种 不 同 形 状的符号 将桥 梁 区 分 为人行 桥 ，车行 桥 和 双 层 桥等。是什么意思？

Difficult to eleven their properties by using the diagram does not necessarily need to understand the detailed features and so it was a common symbol mapping object classification and hierarchical representation of the abstract to describe a map class-level object object. For example, to distinguish

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On the map is very difficult to express their characteristic one by one with the chart, therefore also not necessarily needed to understand the so detailed characteristic to appear has carried on abstractly the classification, the graduation expression method namely with the charting object has the

Maps difficult to express their characteristics each figure, does not necessarily need to know the detailed characteristics of drawing objects that appear on the classification, grading methods with abstract symbols common to describe a certain type of object class and object. For example using two

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