The land is not perfectly arable land. I believe at closer look, the black is a body of water. There is evidence of this in the south part of the body of water that looks like the outlet. Other black patches on other land would be ponds also. The black strip to the right is a canal of water.

Beside many ponds are low areas of wetlands. That is my guess anyway from a farming background.

'Scroll Lock' is not a Mac thing. It should be on most PC keyboards. Then again, your question proves the point of the cartoon. Were you doing that as a joke?