When labeling a polygon using either the Standard labeling engine or the Maplex labeling engine, the label automatically is placed at the best possible location on or near the polygon based on the label parameters that were defined.
There is no setting to allow placing the label at the centriod of the polygon. Instructions provided describe creating a point feature class at the polygons centriod and then labeling the point feature class.
A. Open ArcToolBox and navigate to Data Management Tools > Features and click on the Feature to Point Tool.
B. For the Input Feature Class, select the Polygon Feature class; the Output Feature Class should automatically default.
C. For the centriods to always fall inside of the polygon, check on 'Inside'. If the Inside option is not selected, some of the centriods may not be placed inside of the polygon, for example, with U-shaped data.
D. Add the points to the map.
For ArcEditor and ArcView:
A. Calculate the centroid of the polygon by adding a Latitude and Longitude field to the polygon Attribute table. See the link in the Related Information section below.
B. After the Latitude and Longitude fields have been populated, navigate to Options > Export > Export All Features into a new .dbf.
C. Add the new .dbf to the current map.
D. Select the Source tab, located at the bottom of the ArcMap Table of Contents (TOC), to see the .dbf.
E. Right-click on the table that appears in the TOC and select Display XY data. The X field should read Longitude and the Y field should read Latitude.
F. Click Edit and select Import. Import the current coordinate system from the original polygon Feature Class, and click Ok.
G. Export the event theme to a shapefile or feature class to label the polygon centriod using the points created previously. Right-click on the Name_of_Table Events layer and select Data > Export Data. Export all features using the same coordinate system as this layer's source data into a new shapefile or feature class and then add the new points feature class to the map.
H. Remove the .dbf and the Name_of_Table Events layers. The map should contain the polygon feature class and the points feature class.
Navigate to View > Toolbars (Customize > Toolbars in ArcGIS 10) and select the Labeling Toolbar.
Click the Label Manager button
on the Labeling Toolbar.
Under 'Label Classes', click on the check box for the name of the Point Feature class. Highlight the default label class that appears under the name of the point feature class to see the label options on the right-hand side of the screen.
Specify the Label Field. Under Placement Properties, select the 'On Point' option to force the label to appear directly on the point. Click OK to close the Label Manager.
Right-click on the name of the point feature class in the TOC and select Properties.
Select the Symbology Tab. Under 'Symbol', click on the symbol being used to represent the point to open the Symbol Selector.
In the Symbol Selector, click on the Properties button and change the Color and Outline Color to 'No Color' and click OK to close all dialog boxes.