| 摘要 |
PURPOSE:To compactly keep the size of map data which indicates maps and to improve the display speed. CONSTITUTION:The device consists of a map data storage means 1 which stores map data, a map data retrieval means 2 which retrieves map data that are required to display a map including the region of a specified point, a map plotting means 3 which plots retrieved map data, a water system plotting means 5 which plots water system data in the region for which map data are not retrieved and a map display means 4 which displays the plotted map. The feature of this device is that water system data are displayed in the region in which no map data exist, no retrieval can be performed, is considered as a water system. |
