| 摘要 |
In a Geographic Information System, a computer retrieves records from a data base for each map feature that lies within the extent of the displayed portion of the map. The records for point features are organized in "flat" structures where each map feature is represented by a single symbol, and in multi-level "hierarchial" structures where each feature is represented by a hierarchy of symbols representing different resolutions of the map features. For a hierarchial symbol structure, the level of records retrieved by the computer is determined by the scale of the map displayed to the screen. The computer determines, for each symbol at the particular map scale, whether the symbol extensively overlaps any other symbol The symbols that overlap significantly are modified to reduce the clutter by either merging the overlapping symbols into a single symbol including a numeric identifier or replacing the symbol and its siblings by the single parent symbol in the hierarchy. The symbols from the modified record are displayed to the screen.
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