Knowledge Base - Technical Articles


Technical Article   HowTo:  Convert Area into Acres

Article ID: 27851
Software:  ArcGIS - ArcEditor 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcInfo 8.0.1, 8.0.2, 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcView 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3, 9.3.1, 10
Platforms: N/A

Summary

Instructions provided describe how to convert values in the area field into acres.

Procedure

If the data is stored in a geographic coordinate system, which uses units in decimal degrees, the data must be projected to a projected coordinate system which uses a linear unit of measure like meters. Because decimal degrees are angles, an area calculation based on decimal degrees cannot be converted to a usable unit of measurement.

Refer to article 24646, 'How to select a suitable map projection or coordinate system' in the Related Information section for more information about selecting an appropriate projected coordinate system for data.

  1. Calculate area of polygon features.

     Area for polygons in a geodatabase feature class is calculated automatically by the software

  2. Create a new field named Acres in the attribute table.

     Define the new field as DOUBLE. The precision is the length of the field, and the scale represents the number of decimal places. A precision of 18, and scale of 3, for units of feet or meters in a projected coordinate system should accommodate the values to be stored in this field.

  3. Calculate the value for acres for the field by applying the appropriate conversion, such as square feet to acres or square meters to acres.

    Conversion factors:
    • square feet * 0.000022956 = acres
    • square meters * 0.0002471054 = acres
  4. In ArcGIS Desktop at version 10, the Calculate Geometry option in the Attribute Table can also be used.

    a) If the data are in a geographic coordinate system, set the coordinate system of the ArcMap data frame to a projected coordinate system. Go to View > Data Frame Properties > Coordinate System tab > Predefined > Projected Coordinate Systems and select a suitable coordinate system for the area in which the data is located.
    b) Add a field named Acres to the attribute table, as described above.
    c) Right-click the Acres field, and run the Calculate Geometry utility using the data frame's coordinate system.

Related Information

  • Projection Basics: What the GIS professional needs to know
    The following concepts are fundamental to understanding the use of map projections in ArcGIS. 1. Coordinate systems, also known as map projections, are arbitrary designations for spatial data. Their purpose is to provide a common basis for comm...
  • Select a suitable map projection or coordinate system
    A map projection is the mathematical process of taking a view of a spherical globe and drawing that information on a flat piece of paper. Four properties apply to map projections: {PRE}SHAPE DISTANCE AREA DIRECTION{/PRE}To select a ma...

Created: 10/8/2004
Last Modified: 7/5/2011

Article Rating: (1)
If you would like to post a comment, please login

Comments

By Anonymous - 05/12/2005 9:37 AM

WHAT IF YOUR DATUM IS USING A STATE PLANE COORDINATE SYSTEM SUCH THAT YOUR UNITS ARE NOW GRID FEET AND YOUR AREA IS NOW GRID SQ FT. TO OBTAIN ACREAGE YOU WOULD HAVE TO CONVERT THE GRID FT TO GROUND UNITS OR CONVERT THE EQUIVALENT GROUND ACRE (43560 SQ FT) TO A GRID ACRE (43560)(SF)^2; WHERE SF IS AN APPROPRIATE SCALE FACTOR FOR THE VICINITY OF YOUR SELECTION.

Rating: