Mexico City: The World's Widest City by Diameter

Mexico City spans ~140 km (87 miles) in diameter, making it the widest urban agglomeration globally. Its metropolitan population exceeds 21 million. The Valley of Mexico's basin geography allowed radial expansion, absorbing surrounding towns (Ecatepec, Nezahualcóyotl, Naucalpan, etc.) into a continuous built-up area. Challenges: water scarcity, subsidence, traffic, air quality—managed via massive engineering (e.g., deep drainage tunnel, Metro expansion).