iPad devices only have internal GPS with cellular version. it has been this way always. The GPS works without a cellular
contract or any contact with a cellular
network. So it will provide a position fix anywhere on earth.
Assisted GPS is for when the cellular
network is available. Then the network knows the approximate location of the device. With that information the time to acquire an initial position fix is greatly reduced. Sometime it can take an iPad GPS receiver without cell
service a minute or two before it can make the first fix after turning on location services. Internal GPS draws a lot of
power from the
battery so assisted GPS basically is a feature to save
battery. But it only works when there are cellular sites nearby and you must pay for cellular
service as well.
Many people use apps on tablets for voyage planning. No need for GPS to do that.
But experienced cruisers generally end up feeding all
boat data such as
AIS, GPS,
weather data,
engine data,
water data and even
radar through a wifi access point. This is not expensive. Then every device on board can use that data. And none of those devices have to waste
power firing up an internal GPS receiver. These days,
AIS information is every bit as important as GPS. It's great to know where you are but your eyes can tell you that. It's even better to know where are the big ships over the horizon and where they are headed. AIS can give that information. So any
navigation app that doesn't support AIS data should be placed lower on the priority list.
And before someone pipes up that AIS data is available on the
Internet be aware that data is not real time and can't be depended upon to be as useful as one might think.