Question

It is on the east coast.​

Answer 1

Answer:

What Is In East Coast???

Answer 2

It really depends on common usage around the headword. All of these are common usage:

I live in the east.

I live on the east coast.

I live in the east coast city of XXX.

I live on the outskirts of the east coast city of XXX.

I live in the suburbs of the east coast city of XXX.

We tend to use on for lines or borders between areas (hence on the border).

Note: I have a house on Lake Como (it's not actually on the lake; it's on the line around it).