The United States government put up a building near Sioux Falls. Inside was the biggest computer in South Dakota. The year was 1973. The place was the EROS Data Center. "EROS" is a short way to say Earth Resources Observation Systems. The center is still there today. Its computers receive signals from satellites high above the earth. Then the computers turn the signals into pictures of the earth. Scientists learn much about the land this way. They then help other people take care of resources like water, soil, and minerals. Today, more than six hundred people work at the center. It now has more than twelve million images of the earth. This one shows Lake Oahe on the Missouri River.

Lake Oahe
Photo from United States Geological Survey booklet (1998)