How to play with others

You will need an Origin account and be online in order to start the game. Once playing, you will be able to disconnect from the internet and continue playing in offline mode.

Source

Edit:

Unfortunately, you won't be able to play for long periods of time in this way. This Digital Trends Article says:

Maxis responded that players who lose their connection mid-game will be allowed “to play for as long as we can preserve your game state” a period that will “likely be minutes.”

So it appears that the answer is no, any offline play would only be possible to preserve your game during a temporary disconnect.

You can gift any of the 10 commodities to any other city in your region that has a road or rail connection. You can also gift cash.

To do this, go to region view while loaded into the city you wish to send the gift. Once your camera pans out, select the city you wish to receive the gift, but do NOT load it. Once the city is selected, click the gift button on your toolbar (it will be the farthest icon on the right). This will allow you to send anything your host city has in stock to the remote city.

A couple of caveats:

• The host city must have the item in supply at a trade depot or at a place of origin. Such as the coal mine or oil well. The host city also must provide a vehicle for transport (each of these sources has 1 by default, more can be added via module).

• The destination city must have a place to store the item, such as their own trade depot with the appropriate module OR a building that can receive it (in this case, the smelter).

• Gifting is not instant. The item has to actually be physically loaded into a vehicle and transported to the other city. I like to wait for the notification at the top of the screen confirming that a "gift has been sent to city X". By the same token, the other city will take a bit of time to receive the gift as it is in transit. When the gift is received, you will also get a notification.