The complexity in low altitude has hindered the development and utilization of low-altitude airspace resources with UAVs as the main application users. With the rapid increase of UAV numbers and the rapid expansion of commercial application of UAVs, the conflict between the increasing flight demand and the limited flight space is increasingly prominent at low altitude. Therefore, how to conduct the activities of UAVs at low-altitude safely and efficiently is a problem to be urgently solved. Many countries or regions are looking for solutions. Among the proposed solutions or methods, the low-altitude public air route network of UAVs, which is proposed firstly by the Chinese Academy of Sciences (CAS) to orderly manage UAV low-altitude traffic and efficiently utilize low-altitude resources, has been widely recognized. However, the concept is still in the early exporting stage and is not clear on how to construct. In addition, how to quickly acquire high-precision geographic information to support safe and efficient flights of UAV in low altitude, especially in urban areas with complex and high-dynamic changeable surface environment, is also difficult. In view of the promising application of remote sensing (RS) technology in extracting and processing air route sensitive elements, this paper proposes a method to efficiently and iteratively construct the low-altitude public air route network by RS and geographic information technology in urban areas, and then demonstrates the feasibility of this method from theoretical support and existing research foundation. The technical roadmap includes four steps: (1) generating the first-level air route network based on ground roads to make full use of ground traffic facilities; (2) constructing the second-level air route network by using positive constraints of air routes, such as green lands and waters; (3) constructing the third-level air route network by avoiding negative constraints of air routes, including buildings, weak-communication areas and power lines (poles); (4) generating the fourth- and fifth-level air route network by simulated flight and practical flight tests. Comparative analysis between actual measurement and simulated environment map is conducted to ensure safe UAV flights. The method proposed above comprehensively utilizes interdisciplinary technologies such as RS, geographic information system (GIS), aviation and transportation, and provides a new way to make safe and efficient UAV operations in low altitude. Furthermore, this paper uses geography method to construct UAV air route network in low altitude, which is another breakthrough in the application of UAVs in geography after UAV remote sensing application. It also expands the research scope of geography and will certainly promote the development of geographic science.