[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.
If both demand and supply decrease, consumers wish to buy less andfirms wish to supply less, so output will fall. However, since consumers place a lower value on each unit, but producers are willing to supply each unit only at higher prices, the effect on price will depend on the relative size of the two changes.