University of Guelph Library
This help page will describe how to calculate area for polygons from a shape file.
Assign a Projection for the Shape File
(If it hasn't been done already).
- Add the shape file containing polygons to ArcMap. Re-project the shape file from Geographic to a Metric Coordinate system such as Universe Transverse Mercator, NAD93.
- Right-click on the Layers Data Frame and select Properties. In the Select a Coordinate System click on Predefined – Projected Coordinate System – UTM – NAD 1983 – UTM Zone 17N.
- Choose the shape file in the ArcMap Table of Contents, right-click and choose Data – Export Data – Use the Same Coordinate System as the Data Frame.
- Save the Output shape file as xxxUTM.shp.
- Add the exported data file as a layer to the map.
Calculate Area
Calculating area of polygons can be done using the Field Calculator.
- In ArcMap, open the attribute table of the projected shape file. Right-click on the layer – Open Attribute Table. Click the Option button and choose Add Field.... In the Add Field dialog box type or choose:
- Name: AreaSqKm
- Type: Double
- Precision: 16
- Scale: 8
- Click OK.
- Click on this new column header — AreaSqKm — to make it the active field.
- Right-click on the header and choose Calculate Values. Click Yes to continue. The Field Calculator box will appear. Check the Advanced Box and write the following expression in the Pre-logic VBA Script Code text box:
- Dim Output: as double
- Dim pArea: Iarea
- Set pArea: [shape]
- Output: pArea.area
- Write the following in the Calculation expression for AreaSqKm =:
- Output/1000000.
- Click Apply and OK.
The area by square kilometer has been calculated for each of the polygons in the layer.
Data Access
Contact
519–824–4120 ext. 56417
Visit
The DRC is located behind the Research Help desk in the McLaughlin Library.