His work got attention online last year when he posted maps that showed where tourists photograph a city vs. where locals photograph a city. The spider web of blue dots for locals and red dots for tourists evoke the questions: Which attractions do red dots cluster around? Which sites do the blue dots know that the red dots don’t?

Fischer next tackled racial divisions in 109 U.S. cities, the bunches of colors showing the still-present divisions of race. His latest maps, called “See something or say something,” compare where people write about their social lives (tweeting) and where people photograph (posting to Flickr).

Fischer wants his maps to encourage people to get out on the streets and explore the contours of cities.

“I want people to look at the areas of the maps they know well and look at what makes some places popular and some not popular,” he says. “If you live on a street and no one goes there, what is it that makes people not want to go there?”

What he has observed: People take vacations where they can walk to sites but often live where they cannot; they cluster in neighborhoods with small building plots, narrow streets and wide sidewalks; they photograph older neighborhoods, built before freeways carved through cities.

He lives in Oakland but spends whatever time he can in San Francisco, walking the city, plotting his own march on a Google Map, trying to blanket every street to understand his surroundings. He wants to know what keeps certain neighborhoods alive, what makes others die, and what can be done to help some places come back to life.