Look How Much San Francisco Has Changed In 3 Years

Three years ago, Twitter announced that it was moving into a deserted building in one of the worst parts of the city.

Twitter made the move because the City of San Francisco had created a new tax-free zone in that neighborhood, known as Mid Market.

We took a walk around the neighborhood in July 2011 to see exactly what Twitter was getting itself into. It didn't look pretty. But Twitter made the move, and a bunch of other tech companies followed. Then came the residential developers. Then the other businesses.

Three years later, the change is startling. See for yourself...