The phrase "a flat expanse of" is correct and usable in written English.
It can be used to describe a large, level area of land or surface, often in a geographical or artistic context.
Example: "The artist captured the beauty of a flat expanse of desert in her painting."
Alternatives: "a level stretch of" or "a smooth area of".
What's left is a flat expanse of landfill that is pockmarked with abandoned Coast Guard buildings.
And I'm a guy who thinks dunes give more character to a beach than a flat expanse of sand".
Where a flat expanse of mud flats, salt pans and fish farms reaches the Bohai Gulf, a vast ship looms through the polluted haze.
Still under construction, the park, for now, offers three portable toilets positioned on a flat expanse of green just yards from the waterfront.
The landscape here feels alien: a flat expanse of twisted, bleached-white trees and hunched rock formations that evoke images of a prehistoric time.
Carroll thinks the end is nigh for our now-decadent secular humanism, and starts as he means to go on: "Our culture is a flat expanse of rubble".
For now, I'd advise road-trippers to enjoy what you can on pavement, then retrace and loop inland to Hasik, where the road runs along as beautiful a beach as I have ever seen — a broad, flat expanse of sand and glorious surf — under towering headlands that recall the Cape Peninsula of South Africa.
Stackpole's design was abandoned in favor of a largely flat expanse of poured concrete.
The car feels a bit dated, particularly its flat expanse of dashboard and rather cheap-looking interior materials.
It was a brisk day, and the flat expanse of Table Mountain was bathed in the cool light of the Southern Hemisphere, and so was the harbor, which was full of tourist boats and fishing trawlers.
But it turned out to be the internet that changed the world, while games simply turned to Renaissance perspective to make the flat expanse of a screen seem deep and spacious.
