Setting default units for Shape_Area to be Acres using ArcMap

Question

When I create a new feature layer polygon, how do I set the default in Shape_Area to read out in Acres?

Answer 1

You can't. The Shape_Area/Shape.Area field is built into geodatabase layers and will give area in square units of whatever linear distance unit the feature class uses.

So if your data is in meters, the Shape_Area/Shape.Area field will show square meters.

Answer 2

Shape_Length, Shape_Area, OBJECTID, and SHAPE (among a few others) are all ArcGIS system fields that you don't really have any control over. You could alter the appearance of the number, but since you want to do a unit conversion it isn't possible with that field. As Dan C mentioned, the units are the default units of whatever CRS your data is in.

If you want to display an acreage, you'll need to add a new numeric field, right-click on the header in the attribute table, and use either the Field Calculator to convert Shape_Area to acres, or more simply Caclculate Geometry to directly fill in the values.

Two things to keep in mind. This field will not automatically update if the shape changes - you must manually re-run the calculation. Also, calculating areas is best done in a Projected Coordinate System rather than a Geographic one.

Answer 3

Here's how you can get Shape.area to display acres if it's in another unit. In ArcMap, go to the layer properties and the Fields tab. Under "Appearance", click "Number Format". Click the little button with the ellipses that is now displayed. Or right-click a field name in the table view, go to Properties, and click the little ellipses button next to Number Format: Numeric.

Next, change the Category from Numeric to Rate. You'll have to determine the appropriate Factor for your data. The default distance unit for my data is feet, so my Factor will be however many square feet per acre. So in my case I put 43560 as the Factor. Now I can set whatever other numeric display options I want then click OK to accept the changes.

Now the geodatabase-managed Shape.area field will display my units as acres instead of square feet. Just remember that this only temporarily changes the display of the numbers on the layer in ArcMap, it doesn't actually change the underlying numbers.