Demand means not only having the need to purchase a commodity, but the ability to purchase. The consumer's spending power is determined by the amount of disposable income available to him. The higher the purchasing power the higher the demand, therefore, the higher the supply. Little disposable income translates into reduced supply of fast foods owing to a reduced number of people opt for cheaper options.
The culture of a people determines every aspect of their lives including their eating habits. Setting up a fast food outlet in an area where there is a large number of health conscious people affects the type of fast food supplied. You have to consider whether or not the majority of the population is vegetarian or whether they prefer red to white meat. Peoples' cultures dictate their eating habits and provide a diversification of the fast foods supplied in these areas.
The demography of a population determines what foods are preferred. Cities are good markets for fast food outlets as they have a larger number of young people who prefer dining out, especially in fast food outlets. To maximize on such a market and meet the supply demanded, fast food brands open up branches all over these areas.
Fast food outlets rely indirectly on the weather for them to meet the supply demanded by their customers. Drastic weather changes resulting in floods or famine cripples the supply of these outlets as it means that the raw materials, in this case being chicken, beef, fresh vegetables and flour, are produced at a minimum or not produced at all.