The average pedestrian meandering through urban spaces such as Manhattan’s Washington Square Park or San Francisco’s Embarcadero isn’t calculating the ratio of vertical to horizontal building surfaces or the percentage of tree coverage. But MIT building scientist Christoph F. Reinhart is, with an eye to creating seductive city spaces that also support sustainable energy.

Over the next two decades, the United Nations expects an additional 1.7 billion people to converge in the world’s cities. With buildings already accounting for some 40 percent of carbon emissions in many countries, Reinhart, associate professor of architecture, believes there’s an undeniable need for sustainable urban growth that works across climates and cultures.

Reinhart, who leads MIT’s Sustainable Design Lab, has created a new modeling system called umi (pronounced ooh-me), which, unlike existing tools that analyze an individual building’s energy outlay, allows design teams to model and evaluate dozens or even hundreds of buildings at a time (http://urbanmodellinginterface.ning.com/). He sees umi enabling city planners and architects—for the first time—to improve the performance of their designs at both building and street scales.

Reinhart grew up in Düsseldorf, became a physicist, and studied and worked for a time in the beautiful university city of Freiburg, where he saw people getting around by walking, taking the tram, or cycling on plentiful bike routes. He decided to switch his focus from photovoltaics to architecture when he realized that architects and city planners propel a lot of the decisions that drive the construction of energy-efficient buildings and usable, sustainable urban spaces.

Cities such as Freiburg, New York, Paris, and Copenhagen cater to pedestrians, but “there are examples of how not to do it all over the world,” Reinhart points out: urban spaces lacking trees, or shelter from heat, cold, and wind. Cities need comfortable open spaces, he says, where people simply feel inclined to spend time outside, as well as buildings that work with their local microclimate.

There are strategies for accomplishing this—solar cells, natural interior lighting, bike paths, for instance—but without metrics, policy makers don’t know where to concentrate their efforts. “We want to work with cities to build umi models of their existing structure and use this for future policy decisions,” Reinhart says. Umi currently has several models that allow users to estimate operational energy use of buildings and daylight availability throughout a city, as well as how walkable a neighborhood is.

While umi is a more specialized simulation environment for urban planners and architects, Reinhart’s group also collaborated with Mapdwell LLC to develop a “lightweight” version of umi, a solar map for Cambridge that helps residents identify which roofs are best suited for solar panels; how much the panels would cost; how much revenue they would generate; and whether they could handle peak loads. Umi collects data that could help determine if people would walk to a planned shopping area or commute on a proposed bike path.

The model is already at work in Cambridge, Mass., where an umi solar map, accessible to the public through an interactive web site (http://en.mapdwell.com/solarsystem/cambridge), points out in vibrant yellows, reds, and blues the city’s hot and cold spots—buildings that “leak” heat, blocks that tend to bake in the sun, or suffer arctic-like chill in winter.

“When you see that color heat map, it’s very powerful,” Reinhart says. “If you are the owner of a building that’s red, it can trigger all kinds of discussion…and action.” Fundamentally, urban modeling tools such as umi and the Cambridge solar map provide visual, easy-to-interpret tools that make it easy to talk intelligently about design and to help put buildings together so the result is more livable and more environmentally sustainable.