Creating hillshades from mosaicked 10m DEMs across UTM zones

[Maryrose_Kulick]

Hello!

I am attempting to make a set of large hillshades in ArcMap for California (split into 6 zones). I downloaded 10m DEMs for every county from NED. I created mosaics for each county, and then mosaicked groups of counties into larger regions. I then ran the hillshade tool (with default settings) for each region, but ran into this grid issue (see screen shot).

The grid only appears where I believe there are differences in origin coordinates systems. The DEMs are split into UTM zone 10 and 11 across the state, and I think the merging of these is causing the issue. In one of my hillshades, where all the DEMs are in zone 11, the problem doesn't occur. 

Any advice on how to fix this? I've tried re-projecting my mosaics into WGS 84 and haven't had luck. Should I start from scratch and project all of the original DEMs into the same coordinate system before mosaicking them? If yes, is there a less-than-cumbersome way to do this? California is a big state.

Many thanks!

I

[Robert_LeClair]

Question for you - are you using a Mosaic Dataset or merging all the DEM rasters into a new single mosaicked raster dataset?

[Maryrose_Kulick]

I am using Mosaic to New Raster. I'm using 32 BIT FLOAT, 1 band, and BLEND as parameters, if that is helpful. Also leaving the spatial reference as the default.

[Robert_LeClair · Accepted solution]

I'd recommend creating a mosaic dataset within a geodatabase using the directions within the online help.  One nice thing about Mosaic Datasets is they work with various coordinate systems with the Image.  It "may" resolve the issue of spanning UTM zones.

[Maryrose_Kulick]

Finally got to try this out and it worked! It was also a much easier workflow to make the mosaic dataset. Thanks so much. 

[Robert_LeClair]

That's great to hear!  I'm glad it worked out.  If you would be able to close this thread by marking the correct answer that way it documents properly.  All the best!