Farming has been used by real estate professionals since the 1950's. Before that all real estate transactions were handled by bankers, attorney, and accountants. If someone was moving these were the people who knew about it first and made all of the arrangements. Even if you were relocating to a new city or state these people would call their connections in the new town and someone there would handle it for you.
As more real estate offices opened up it became necessary to divide the work into areas or territories. This became known as farming. The owner of each office would assign a farm to his agents and they worked in that neighborhood, helping the homeowners to list their homes and look for a new one.
This was accomplished by walking through the farm area regularly to speak with the homeowners and to introduce yourself to anyone who did not yet know you. The real estate agent would follow up with a phone call and then a letter or postcard. The agents would give small gifts to the homeowners at various times of the year. These gifts would have the name, address, and phone number of the agent and their office. This made it easy for the homeowners to call the agent without having to look up the number.
This practice continued well into the 1990's. At that time computers and other technology began to surface and suddenly it was possible to contact more people in less time, and for less money, than ever before.
Even with the new technology it is still a good idea to walk through your farm two or three times a year. This will help keep you informed of what is going on in this area and what needs the homeowners may have.