How does the Nikon AW100 use the A-GPS file to help determine position faster?

Hi,

I received my new Nikon AW100 GPS enabled camera yesterday. I had been using a Canon PowerShot SX230 HS GPS enabled camera before then.

I have found the GPS on the new Nikon AW100 to lock on to the satellites much faster even without downloading the A-GPS.

In the owners manual for the Nikon AW100 it gives this link to download the A-GPS file.
http://nikonimglib.com/agps/index.html.en

In the Nikon AW100 owners manual it also notes:

The validity period of the A-GPS files is seven days. The validity period can be checked on the updated screen.

Once the validity period of the A-GPS file has expired, tracking of the position information will not become faster. Updating of the A-GPS file before using the GPS feature is recommended.

Some questions I have about the A-GPS file.

1. How does the Nikon AW100 use the A-GPS file to help determine position faster?
2. Why does the validity period of the A-GPS file seven days?
3. What does 'validity period' mean?

4. Does Nikon have to update the A-GPS file on the download page every seven days?

I have never even heard of A-GPS file until I started reading the owners manual for the Nikon AW100 camera so any information you could give me one how it all works would be greatly appreciated.

Thanks,