From the Presidential Inaugural Committee (PIC) for those attending in person:
“Tickets are not required to view the swearing-in ceremony from the National Mall. Ticketing information for the ceremonial swearing-in is handled by the Joint Congressional Committee on Inaugural Ceremonies (JCCIC) here.
The ceremony will begin at 11:30 a.m., but we [PIC] recommend arriving as early as possible as both ticketed and non-ticketed areas are first-come, first-served.
Please be prepared to be outside for a long period of time and dress warmly. A limited amount of food and beverage vendors may be available, but attendees are encouraged to bring snacks and beverages in order to stay healthy and hydrated.
Ticketed attendees:
If you are attending the Swearing-In ceremony and have a ticket, please follow the instructions provided with your admission ticket. Entrance will only be granted at the gate indicated on your admission ticket.
Non-ticketed attendees:
The non-ticketed area of the National Mall begins at 4th Street NW.”
Full version of the map: