數值資料是地理資訊系統運算的基礎，資料之內涵誤差(Inherent Error)及處理誤差(Processed Error)，可提供使用者成爲運用、評估、決策的重要考慮因素。利用掃瞄機得到高解析度、高精確度的數化地圖資料，如影像地圖，在導航中可以提供應用系統重要地物、目標區背景之顯示。然而經過幾何轉換及重取樣的過程後，圖內空間物件(spatial features)的偏移量是否在容許誤差內，就得先經過精度評估方能決定。本試驗乃以標準網格線之相對位置（座標），來檢驗地理定位轉換後影像中X、Y座標與其應有座標之差異量，將全幅圖平面誤差分佈情形做數字及圖形的表示。相同流程，亦可配合高精度之檢核點（由GPS測得），評估已數化圖檔之精確度。使用者不僅可參考分析報告，對於全圖之精度良窳，亦可得到直接立即的確認。

Numerical spatial data builds the foundation of Geographic Information System (GIS) Data contains inherent errors and processed errors which provied information for manipulation, assessment and decision_making of geagraphic features. Digital image maps, digitized by scanners, provide the system presentation background in tour guiding system which combined with a Global Positional System (GPS). The aim of this exercise is to obtain the error distribution of whole maps, according to the measurement of difference between mesh data and geo-referenced images to assess the positional accuracy of digitized maps. People can legibly refer to the analysis reports and the corresponding error image, while considering the suitability of application of data rescource.