Merging DEMs
For the purposes of contour creation, temporary rasters can be generated using the original digital elevation model (DEM) files. When the DEMs are merged, they are combined into a single new DEM that can be used for contour generation without modifying your original DEMs.
Steps:
- Start ArcMap.
- Load the DEM files you want to use to create contours.
- On the main menu, click Customize > Toolbars > Production Contouring.
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Click the Merge and Filter DEMs button  on the Production Contouring toolbar. on the Production Contouring toolbar.The Merge and Filter DEMs dialog box appears.  
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Click Merge Only in the Operation area. 
 Tip: Tip:You can filter the merged layer at the same by choosing the Merge and Filter Result option. 
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Click the Open button  next to the Merging/Filtering Output Raster Workspace field. next to the Merging/Filtering Output Raster Workspace field.The Choose DEMs Folder dialog box appears. 
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Navigate to a current DEM folder. 
 Note: Note:The folder you choose must be a preexisting raster workspace. 
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Click Open. 
The Merge and Filter DEMs dialog box appears. 
- Type a name for the merged file in the Merged Output Name text box.
- Click OK.
7/31/2012