Overlay Analysis: Union Map

Aim:

To create perform overlay analysis of two (digitized) Feature datasets, using  Union method.

Procedure:

Concept:  Union is simple and straight. It’s a direct union or two or more selected layers.

Step 1: Map Input

Identify the two layers that can be digitized from your toposheet or base map. For this session, Forest Area and Waterbodies (Perennial) were digitized from the given topographic map of Nellore & Cuddapah Districts.  The Polygon Entities were saved into respective shapefiles in target ArcCatalog Folders. 

Step 2: Map Processing

• ·         Digitize the Polygon features for selec
  
  ted entities. Perform Attribute Editing. “Add Field” for “Name” and “Area”.  Specify the Names and calculate geometry to calculate shape area.  (note to calculate geometry, the features need to be on Projected coordinate system).
• ·         Locate the “Union” tool in Analysis -> Overlay, toolbox.
• ·         Define the Tool Input Tool Input “Forest” and union feature as “Waterbodies”  and specify the target output folder.
• ·         Click “Ok” to generate the map output

Step 3: Map Display

Create Custom Map Layout with the necessary map elements and Export map to Jpeg format. It’s best to display map outputs in three data frames, one for the Overlay Output ad two for displaying the input feature classes.  One may also choose to Add Attribute table to layout, an option available within the Table options.

Conclusion:

Union map for the chosen polygon attributes layers are generated using ArcGis 10.1.