This thesis addresses the relationship between the physical dimensions and aspect ratios of urban areas and the airflow below the urban canopy height. The aim is to investigate the link between these aspect ratios and the resulting airflow patterns, wind speed and direction, and pressure coefficients on the envelope of target buildings. The research method involves several steps which seek to explore the airflow in four urban scenarios, simplified simulation using two parallel bricks; several complex urban prototype scenarios; and two actual urban areas used as case studies situated on the Cardiff Cathays Campus and the Paulista Avenue - São Paulo. The research methods employed are: atmospheric boundary layer wind tunnel (WT), steady-state standard k-e CFD simulation and field measurements (FM). Three prevailing wind directions were investigated: parallel, orthogonal and oblique. The outputs are guiven in terms of: Cp and ΔCp data displayed as graphs, tables and/ or contour plots; airflow patterns and velocity magnitude and direction, displayed as vertical profile graphs and visualized by means of CFD pathlines or WT helium bubble pathlines; and correlation displayed as scatter diagrams and matrices. A relationship was found between the urban aspect ratios and the ΔCp results. This was demonstrated by statistical methods using the data on the variables concerned, thus verifying the strength of the correlation between them. Strong correlation was found between the investigations into similar scenarios of the urban prototypes and the two case studies as regards both the aspect ratios and the ΔCp results. On the other hand, low correlation for the same variables were identified when contrasting dissimilar urban prototype scenarios. Moreover, good levels of comparison were found between the FM and the CFD simulations in Case Study 01 for both the decrease in wind velocity magnitude and direction in urban areas.