http://blog.xuite.net/joy715/blog/16369373/track
有網友問到如何計算甜甜圈狀的面積(大圓減小圓的面積)或是大框減小框的面積？
原則上甜甜圈應該是可以用繪圖功能畫出來，然後用面積計算的方式算出面積。詳細計算面積的操作步驟如下。
以下內容轉錄自Calculating polygon area in ArcMap 。
To create a new attribute field for "area" in ArcMap, follow these directions - note you cannot be in an editing session to do this (don't ask me why):
Open the layer's attribute table in ArcMap
Click on the Options tab
Choose Add Field
Name it Area
For Type, choose Double
Don't put anything under Precision or Scale.
Click OK
Calculating area for polygons (from ArcGIS Desktop Help)
Open the attribute table of the layer you want to edit.
Right-click the field heading for area (if there is no field for area values, you can add a new field for area by clicking the Options button and selecting the new field option).
Click Calculate Values.
Checkmark the Advanced box (this is important - dont' forget this!)
Type the following VBA statement in the first text box (you should be able to copy and paste): Dim dblArea as double Dim pArea as IArea Set pArea = [shape] dblArea = pArea.area
Type the variable dblArea in the second text box (near the bottom of the dialog box) directly under the area field name.
Click OK.
