## 5 Discussion on Relevant Issues  
### Reliability of Research Results and Data Analysis  
This project carefully considered and controlled every step of the process from roof space inventory to agricultural production potential calculation: (1) Considering four obvious factors that affect roof agricultural planting (roof height, slope, area, and building type), a roof space inventory was conducted. (2) By importing Google Satellite Maps into GIS for roof space analysis, various methods such as high-definition satellite maps, Baidu panoramic maps, and on-site inspections were combined to improve the accuracy of the analysis. (3) Referring to multiple data sources, we obtained the annual yield of vegetables per unit area under different cultivation methods through weighted calculation. (4) Based on the inventory data and considering the utilization rate of roof area, the selection of different cultivation methods and production potential calculation for roof agriculture was carried out based on the type of building and roof area. From the above analysis, it can be seen that each step of the research aimed to comprehensively consider the problem, and the data collection and application were rigorous to minimize errors and improve the credibility and reliability of the research results. According to the data from this study, the usable roof area of the Qingdao Shibei District, which covers an area of 66 square kilometers, is 383.3 hectares, accounting for 5.81%. If considering the general urban spatial structure and deducting the relatively large coastal area on the west side of Shibei District (about 1258.91 hectares), the idle roof  
Figure 4: Framework for roof space inventory and potential assessment process methodology; Source: self-drawn. area in Shibei District accounts for 7.2 hectares per square kilometer. New York, which covers an area of 789 square kilometers, has approximately 10,000 buildings, providing 15,481.7 hectares of roof area [22], accounting for 19.6% or 19.6 hectares of roof area per square kilometer. In contrast, the 7.2% inventory result in Qingdao is relatively low. The main reasons are as follows: (1) There are many sloping roofs in the Shibei District of Qingdao, and some old buildings with flat roofs have also been affected by their top chimneys or shapes, which affects their availability. (2) This inventory removed roofs with a height of over 40 m, roofs with pollution that are not suitable for planting, small and fragmented roofs, and prefabricated iron sheet roofs. However, compared to the agricultural area inventory results of Bologna, Italy, the proportion of available roofs in Qingdao is relatively high, with only 82 hectares of roofs available in Bologna, which covers an area of 140 square kilometers [6]. This indicates that the results may also be affected by factors such as urban building density, building characteristics, and inventory methods. During the inspection, it was also found that there was only a small amount of sporadic agricultural planting on the roofs of buildings in the Shibei District of Qingdao, and the roof agriculture was basically in a \"zero state\". [PERSON]'s study of 185 rooftop agriculture (RA) worldwide found that North America has the best development of RA, with 81 RA, 70% of which are open-air farms, of which 26 are in New York and 15 in Toronto [23]. Research has shown that these farms in North America are mainly built to improve quality of life and provide social education, with commercial operation being the second common purpose of farms [24]. Roof agriculture has developed well in developed cities mainly due to the following factors: These areas have good roof space resources, their roof agriculture developed earlier, and they have clear development goals. These country or cities have encouraged and promoted the development of roof agriculture through certain policies [25; 26]. There is no policy related to rooftop agriculture in Qingdao, and overall, urban agriculture in China started relatively late [27].