I am currently doing some exercises to better understand GCS (Geographic Coordinate Systems) and PCS (Projected Coordinate Systems) using data from Hawaii (the whole state, including all the islands). I chose this data since it spans two UTM zones.
Which GCS would I use?
I downloaded data from the state of Hawaii and they are using NAD83. How does an organization choose which GCS to use when there are various ones? Would the state of Hawaii use NAD83 in this case because it is the most recent one? (If this is the reason, what is the purpose of still having the option in GIS to convert to earlier datums, such as NAD27, for example?)
In addition, would I use the Hawaii_Albers_Equal_Area_Conic as PCS? The data I downloaded show NAD83 UTM Zone 4, which I found strange since the whole state spans two zones (Zone 4 and 5). Is it incorrect in this case?