Hi Everyone,

Thanks so much to Theresa Dawson, Averill Cate, Chuck Nelson, Joe Martinetti, Bill Huber, and Mike Price for replying to my question.  Your help is greatly appreciated.

The responses were very similar.  My main problem seemed to be that I created hillshades from my DEMs before I merged them.  I was unaware that the algorithm used for the hillshade function creates a one-cell width "blank" border around the  grid being processed.  (Hindsight makes me wonder why I would go to the trouble of making 20 hillshades to merge instead of merging and then making only one hillshade, but I have a habit of doing things the hard way before I realize the stupidity of it.)  For complete details on merging DEMs check out these two sites:

     http://www.quantdec.com/SYSEN597/How_to.htm : follow the link to "Patch gaps or missing values in grids."  This is from Bill Huber.  It's a great site with lots of info for the novice.

     See an article in ArcUser (Lesson 9) at
http://www.esri.com/news/arcuser/0401/avmodel.html, to learn how to use Phil
Hooge's Merge routine.  Note:  the link for the 'gridproj.avx' extension is not correct so just look it up in ArcScripts to download it.

For my project, I merged my 20 DEMs (UTM meters) with the Mosaic function in the Spatial Tools extension and used the steps discussed in the aforementioned "Patch gaps..." section (Bill Huber).

Thanks again to everyone who replied!  Long Live The List!!!


Christel Braley
Hydrology Tech II (GPS/GIS)
Newmont Mining Corporation
P.O. Box 669
Carlin, NV  89822-0669
Tel:  (775) 778-4887
Fax:  (775) 778-4849
cbra2@nevada.newmont.com