Phildo's got it right. I have 2 singh ray GND's that are the card style. They can either be hand-held or in a mount. I have the the cokin p-mount.
I'll handhold those guys with the UWA for something like this… With the Soft GND. Which as it turns out is a bad example since the horizon is near center...
https://farm4.staticflickr.com/3827/...bf0a9332_c.jpg
or the hard GND in this mounted in a holder. Note the horizon is pretty high.
https://farm3.staticflickr.com/2901/...fd23e4c0_c.jpg
That previous posted North Peak shot had the hard GND at the lake's horizon right side up and the soft GND upside down to stop down the bright grass in the foreground. Just for balance. And that foreground turf still wants to come in a little bit hot. Though well within the histograms tattle-telling…
sorry for the reposts. They are some of the more accessible examples of what we're talking about. And it's nice to add some photos rather than 5 replies of words on the top of the POTD page.