The third house covers communication, such as writing, speaking, editing, research, and translation.
The third house also rules code writing and digital forms—a website, app, electronic game development, social media, and podcasts. The third house also covers teaching, lecturing, and public speaking. Thinking, perception, reflection, and the gathering of facts all come under the third house.
The third house rules negotiation and is the home of all contracts and agreements, journalism and documentary work, and the reporting of news. This house is based in facts. (Other houses in the horoscope cover creativity and imagination.) The ancient astrologers felt the ability to communicate clearly was so important, they designated the topic to an entire house of the horoscope, equal to the other houses.
This house also covers your immediate neighborhood, short-distance trips, and all transportation—ships, cars, rail, buses, and planes. This house comes into play when you are buying or selling a car, booking an airline ticket, or making special appointments and meetings.
This house covers the post office, couriers like FedEx and UPS, messengers, and delivery people.
Another important area that the third house governs is early education. Specifically, this house covers nursery school through kindergarten, and grade school through high school.
It rules your sister and brother and also your cousins. This house will describe the nature of your relationship with these individuals and how you view that person.
Finally, the third house covers your perception of your early childhood experiences, something I discovered by doing hundreds of charts.
The natural rulers of the third sector are the intellectual, communicative sign of Mercury and the sign Gemini.