[Note: The distance between cities in California (US) distance chart below is straight line distance (may be called as flying or air distance) between the two locations in California (US) calculated based on their latitudes and longitudes. This distance may be very much different from the actual travel distance.]
In drawing the demand schedule or the demand curve for a good we take income of the people as given and constant. When as a result of the rise in the income of the people, the demand increases, the whole of the demand curve shifts upward and vice versa. The greater income means the greater purchasing power.
Supply and demand curves express relationships between price and quantity. Equilibrium exists when supply equals demand. The shape of these curves and the equilibrium price affect small and large businesses because revenues are a factor of price and quantity. Although a single business cannot affect the shape of these curves, the combined actions of businesses and consumers affect the supply and demand curves for different industries.