"Seniors and mothers pushing strollers say they’re grateful": Why a Seoul National University returnee created 'Geuneullo'

[Financial News] The heat wave that pushed temperatures above 40 degrees Celsius in some areas last week appears to have eased somewhat over the weekend. But the heat has not fully gone away. The heat dome that had covered the Korean Peninsula has only loosened for now, and the sweltering weather is expected to continue for the time being.
In fact, the daytime high in Jongno District, Seoul, reached 34 degrees Celsius on the 10th. As the Korea Meteorological Administration (KMA) forecast that the sweltering heat would continue through the end of the month, people who had been badly burned by the life-threatening heat are busy looking for ways to avoid it.
Beyond basic measures such as carrying a handheld fan and a parasol, some people are even developing and distributing apps that show cooling centers or public transit stops equipped with air conditioning.
Among them, 'Geuneullo,' a route-guidance app created by a 23-year-old college student, became a hot topic online last week as the Korean Peninsula baked under the heat wave.
Yoo Min-joon, 23, who developed the app, said in a written interview with this newspaper on the day that "on the App Store, 14,000 people downloaded it over the weekend, bringing cumulative downloads to 65,000, and on Toss, 3,000 people downloaded it over the same period, with a total of 15,000 users now."

'Geuneullo' calculates building shadows that shift by time of day on a map and guides users to the route with the most shade to their destination. By helping people avoid direct sunlight and walk in relative coolness, it drew strong attention among those who get around on foot.
On the 4th, when the heat peaked and temperatures were at their highest, more than 20,000 users flocked to the app in a single day, causing access difficulties.

The person behind the app is Yoo, a 23rd-class student in the Department of Mathematics Education at Seoul National University. He completed his military service in June and is set to return to school for the second semester in September.
Yoo explained the reason he started developing the app, saying, "After finishing my service and preparing to return to school, I went to campus a few times. The walk from class to the subway station, which I took as a way to relax, felt unbearably hot. That was when I thought, 'I really need to make this app now.'"
App development has long been one of Yoo's hobbies.
He started by making an app to check his school timetable and cafeteria menu in middle school. He later created an app that automatically switched a phone to silent mode in public places, as well as a study timer called 'Kkaeumi' that helps users shake off drowsiness. Each of them was an app he either wanted to use himself or that solved an inconvenience, and 'Geuneullo' grew out of that same idea.
Working alone also brought many difficulties. The biggest issue was map data. Domestic map and pedestrian network data were expensive, while public data was fragmented. Yoo lamented, "Since this was an app I started to use on my own without capital, I couldn't subscribe to paid services or negotiate for high-quality materials."

Yoo's app, developed in just two weeks, quickly spread among people tired of the heat. As it was introduced on social networking service as a "smart app for beating the heat," its user base surged almost overnight.
Yoo said, "It had been about two or three weeks since I released it on Toss, and I didn't even know at first. Then a friend sent me an Instagram post, and that's how I found out the user count had increased." He added, "I was happy that more people were using it, but I also felt overwhelmed when it came to handling issues such as app access failures and follow-up updates."
As a developer, Yoo also expects 'Geuneullo' to remain useful even after the heat wave passes. That is because the app optimizes walking routes themselves, not just shaded paths. More importantly, users can search with preferences such as slope, stairs, and congestion, allowing them to choose routes that fit their needs. It is useful for people who have to travel on foot and are vulnerable to transportation barriers.
Yoo said, "I was especially struck by reviews saying people were using it so well on their commute, because that situation is similar to my own walk to school. I was also deeply moved by feedback from seniors and parents pushing strollers or walking with children, saying it was helpful." He added, "The shaded-route feature can be used continuously by older adults, people with disabilities, and those with sun allergies."
He continued, "Because it finds walking routes that fit each person's conditions and provides personalized travel paths, I think people who want to walk on gentler roads without strain will also keep using it." He added, "Since we have already built data and services for pedestrian networks, underpasses, buildings, and public transit routes, we plan to develop it further so that it can provide routes tailored to various situations and individual conditions regardless of the season."

[email protected] Kim Hee-seon Reporter