Retoohs, I don't have the A99, however I think the GPS probably works the same as the A77. It is not absolutely necessary to download the GPS Assist Data, it should still work, however Sony advise it be installed as it is supposed to speed up considerably the acquisition and accuracy of a signal. On the A77 it is found in the Spanner menu 1/GPS Settings/Use GPS Assist. If you have not loaded the assist data or not reloaded it for over a month, it will be turned off. If it is on it will show 'Valid Period' followed by a start date to end date.
For the A77 you must install Sony's PMB or PlayMemories Home software which are pretty poor programs for editing. I only installed PlayMemories Home to get the GPS Assist Data, otherwise I use Photoshop. This software is free for owners of a Sony camera. You may have to register it first, I cannot remember.
From Sony Canada..
How to import GPS assist data to the SLT-A77 camera.
You can import GPS assist data using the Picture Motion Browser (PMB) or Play Memories Home™ software. To import, connect the camera to the computer connected to the Internet. The message GPS assist data will be updated appears and the data will be automatically imported. If the update does not start automatically, install the software and follow the procedure below.
When using the Picture Motion Browser (PMB) software:
1) Turn on the computer.
2) Turn on the camera.
3) Connect the camera to the computer using the supplied USB cable.
A. The camera LCD displays USB Mode and Mass Storage.
B. Any Removable Disk windows that open on the computer screen can be closed.
4) On the computer, start the PMB Launcher.
5) In the PMB Launcher window, click GPS.
6) Click GPS Support Tool.
7) In the GPS Support Tool dialogue box, click the Update Now button.
When using the PlayMemories Home software:
1) Click Install Expanded Features.
NOTE: A message saying Downloading the Installer appears.
The expanded features are downloaded and installed.
2) After the expanded features are installed, click Tools.
3) Click GPS Support Tool.
NOTE: The GPS Support Tool cannot be used with the
PlayMemories Home Lite version.
4) Click Update Now.
This may not apply to the A99.