I'm trying to merge some dems downloaded from USGS. When I used arcgis 9.2 there was an expression to be used in raster calculator to do that. I used it again but unfortunately it doesn't work in arcgis 10.2. What can I do?? I do not have the toolbar Production Contouring
Start by converting them to raster formats (assuming they are in DEM format to start with):
then use the 'Mosaic to New Raster' tool to combine the different rasters into a single one:
Make sure that they are in the same units before mosaicing them or they will look really odd when you stitch them together.
That's the basic approach I use, I'm assuming the DEMs you have are all in the same coordinate system/projection/units/cell size/etc. If not, make sure you get all the rasters into identical formats before you start, it will make your life a lot easier.