Lets take a 1 square kilometer, or 1 million square meter of residential land. If houses are uniformly 500 square meters large including the yard, this fits 2000 houses. If each household plants a leafy tree of any kind in their yards and assuming a full grown tree has a canopy of 3 meter by 3 meters or 9 square meters, the total canopy would 18,000 square meters or 1.8% canopy coverage. Studies indicate that around 0.04 to 0.2 degrees centigrade mid-day temperature reductions occur with every 1% canopy increase. At 1.8% canopy increases this is 0.07 to 0.36 degree centigrade.
Also, apple trees bear 40 to 200 kilograms of fruit per year. If apple trees are planted and each tree yields just 40 kilograms, a 1 square kilometer land can yield 80 tons of apples. Global production of apples is 55 million tons worth US$10 billion. This works out to around US$182 a ton. For 80 tons, this is US$14,545. This is real Urban Farming.