I downloaded NED rasters from USGS, and I now want to mosaic all of the rasters into one. I used the Mosaic to New Raster tool, but the output is a big, black rectangle. Am I missing something? I feel like I might be making a rookie mistake.
ArcGIS Desktop – Fixing Mosaic of Rasters Appearing as Big Black Rectangle
arcgis-desktopmosaicraster
Related Solutions
TO merge raster layer, you can use the Merge raster layers tool. You can get the tool from Processing Toolbox -> GDAL/OGR -> Miscellaneous -> Merge raster layers.
But before the mosaic process, you need to confirm the data type of the raster images. You can check the raster data type from Layer properties -> Metadata, then go to Data Type. In the example below the data type is 16 bit signed integer. Thus, the output data type should be the same.
Here is an example of of SRTM data before mosaic:
- Open the merge tool from
Processing Toolbox -> GDAL/OGR -> Miscellaneous -> Merge raster layers - Select the raster images using the
...dots - Select
Int16(in my case), yours might be different depending on the input data type - Define the output file name with extension such as tif for example.
Here is the output mosaic DEM
In ArcGIS, if your output is a GRID then use the layers Symbology to not display the NoData values as shown below. 
If your output is a single band image you can set Display Background Value as 0,0,0 and as No Color but any pure back pixels will not be displayed not just the ones on the border.
Best Answer
If you have not recalculated the statistics, you can do this by right clicking on the raster and selecting "Calculate Statistics"