Geuneullo bets shade-routing wins Korea's heat: solo student app hits App Store #1

Geuneullo (그늘로: 뚜벅이의 여름길, 'Walk in the Shade') is a free iOS map app that routes pedestrians through shade. It calculates the sun's position and the shadows cast by buildings and street trees at a given time of day, shows what percentage of each route is shaded, and even suggests which side of a bus or subway car stays out of the sun. Yoo Min-jun, a 23-year-old Seoul National University student who commutes from Gyeonggi province, built it in about two weeks using OpenStreetMap and government building, street-tree and transit data, and released it on the App Store in mid-July 2026.

Korea's record-breaking 2026 heat wave, with temperatures nearing 40°C, turned the app into a national story. It spread by word of mouth through social media — 20,000 people signed up on August 4 alone — and navigation-chart downloads jumped from rank 209 on August 1 to 119 by August 3, according to app-analytics firm UPUP. On August 5 it hit #1 in Apple's free navigation chart, ahead of Google Maps, Kakao Map and Naver Map, and by August 6 it was the #1 free app overall in Korea.

The case is a bet that a solo student, not a maps giant, could win the summer by owning one narrow question — where is the shade right now. No company, budget or funding stood behind the app; its edge was public data plus a genuinely time-sensitive problem, and its distribution was the moment itself: when record heat made 'shade' the most urgent query of the day.