This image appears in the 1984 book The Future World of Agriculture and illustrates futuristic farming techniques near a sea city.
Robots tend crops that grow on floating platforms around a sea city of the future. Water from the ocean would evaporate, rise to the base of the platforms (leaving the salt behind), and feed the crops.
Sea City 2000 (1979)
Robot Farms (1982)
Farm of the Future (1984)
Superfarm of the Year 2020 (1979)