To find the area of the entire farm on the map, you can use the formula for the area of a rectangle:
\[ \text{Area} = \text{length} \times \text{width} \]
For the farm, the dimensions are 50 cm by 20 cm.
\[ \text{Area of the entire farm} = 50 , \text{cm} \times 20 , \text{cm} = 1000 , \text{cm}^2 \]
Thus, the area of the entire farm is \(1000 , \text{square cm}\).