Friday, March 14, 2008

To adjust the position of maps in ArcGIS

Here I encounter an interesting problem that two Taiwan shapefile with two different administrative units can not completely overlay to each other (shown in the first figure below). It confused me a lot and made me think that the projection definition can be an issue for these maps. Some solution for the change of projection system in ArcGIS is discussed in this document. The projection definition indeed has some issue in Taiwan area where several definitions exist concurrently and are inconsistent. For the detail information about the projection issue in Taiwan.
  1. Introduction to projection system and definition of two-degree transverse Mercator (二度分帶)
  2. The webpage for the description the three common Transverse Mercator system TWD67 (Taiwan Datum 67), TWD97 (Taiwan Datum 97), WGS84 (World Geodetic system 84)
  3. A very informative educational website
  4. Projection system transformation
However, in fact, the solution of the displacement of these two shapefiles in ArcGIS does not have anything to do with the coordinate systems, according to the experience drawn from the trials by myself and my student. Here is the solution to adjust the map proposed by Chi-Shih
  1. 開啟arcmap選擇a new empty map
  2. 看到一個黃色+號圖形,把這三張圖讀出
  3. toolseditor bars→會出現編輯的工具列
  4. editorstart editing→就可以開始編輯
  5. 先打勾里村跟縣市(或鄉鎮)作對比
  6. 看完對比之後,只那村里勾選→用滑鼠把外島那一部份框起來,移至最左邊,不要擋到其它那兩張圖外島的位置就行了
  7. 然後勾選其它兩張任一張圖,做對比→一一的移動到適當的位置
  8. 完成了之後,到editorstop editing→它會問要不要存檔→ok→即完成


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