Since early times, communities endure through actions that make food and basic needs. When specific products are missing, people have sought out additional communities to acquire these goods.
Quite often, these trading/business actions are finished in particular places like a market place or even a primary street in a city. As time passes, this place becomes known as a meeting place for promotion and company actions. You can buy different products like jasmine green tea through the internet.
As time passes by, permanent structures would be built in these locations. Aside from the basic trading, business establishments such as food and refreshments, delivery services could be set up.
Eventually, many other services to cater to the needs of travelers and business people would also rise up. Perhaps, even housing will follow. This is the precursor of what is now known as a "central business district".
Today, the CBD in essence represents the major financial image of a city. This is where most businesses would locate their offices and where banks would set up their main headquarters if not their biggest branches.
It is likely a center for transportation and communication as well. Since people would travel to and from the place, modern thoroughfares with complete transportation facilities are likely to be found here too.
State of the art communication centers would need to be present for faster and easier access to the world.