Desperate for shade on your walk? There’s (almost) an app for that.

It’s getting increasingly unbearable, even downright dangerous, to walk in cities. That’s because of the urban heat island effect: Buildings, sidewalks, and roads absorb the sun’s energy and radiate it back at pedestrians, raising temperatures far above that you’d find in the surrounding countryside. If a city like Phoenix doesn’t have enough shade, people can’t move safely by foot, when really we need to help folks do more of that, because ambling improves public health and reduces vehicle traffic. If you boot up a maps app on your phone, it provides the most efficient way of getting from point A to point B in a metropolis, but it tells you nothing about the blast furnace you’ll endure along the way. A new research project from Arizona State University hopes to fix that with Cool Routes, an online tool that calculates the heat that you might feel along active mobility paths. In addition to finding the shortest path, it determines the coolest and shadiest — and therefore safest, thermally speaking — one. Though it’s limited at the moment to the ASU Tempe campus, the researchers are open-sourcing the tool for any city to use, and maybe one day popular map apps will incorporate such data too. Your weather app isn’t lying about the warmth, but it doesn’t provide a full picture about the heat load on the human body. Air temperature is just one component of how comfortable you feel: Add high humidity, and 80 degrees Fahrenheit feels more like 100, because the extra atmospheric moisture makes sweating less efficient at cooling the body. A lack of shade makes the heat feel even worse. “That is what makes being in a hot environment dangerous, because we see lower numbers on our phones,” said Isaac Buo, an urban informatics scientist at ASU who co-led Cool Routes with Ariane Middel, director of the university’s SHaDE Lab. Take a diversion into the shade and you reduce the heat load by half. Instead of simply referencing a thermometer, Cool Routes calculates “mean radiant tem