To keep up with world Rapid population growth in many countries including Egypt, the Egyptian government adopted polices to establish new urban communities, which many of them located in severe conditions of hot arid climate. However, the urban plans of those new cities do not prioritize the local climate considerations in its planning, which negatively effect on the thermal performance of urban spaces. In recent decades, greater attention was given to study the relationship between urban features and the local climate, developing mitigation and adaptation strategies with the aim of improving the thermal performance of urban spaces. So, this study aims to formulate a matrix of guidelines for urban heat islands mitigation strategies concerning urban geometry that can be helpful in improving the thermal performance of outdoor spaces in the existing new Egyptian cities -which allocated in hot arid climate zone, to enhance thermal comfort in these spaces.
To achieve this goal, a comprehensive review, and analysis of the impacts of different urban geometrical thermal mitigation strategies on outdoor spaces in hot-arid climate, is presented. The geometrical variables of urban spaces which have been investigated in the reviewed researches classified into two main groups (squares and plazas, canyons). The geometrical variables of squares and plazas include; side compactness, and Sky View Factor (SVF). Canyons geometrical variables are; SVF, aspect ratio and side profile shape. These variables depend on the features of those spaces which resulting from the urban pattern form and geometry. These guided values have been applied theoretically and practically on three real cases, to illustrate the mechanism of matrix guidelines applying on urban outdoor spaces thermal behavior initial evaluation and determine the most suitable environmental mitigation strategies directly. Applying of guidelines help in mitigating thermal behavior of plaza with about 18.73 k degree and the canyon space with 3.28 k degree. The discussion of this research clearly reflects the importance of urban planning guidelines that can be applied to help enhancing outdoor thermal comfort. This study is useful in controlling the climatic consequences of urban planning at an early stage.