For the first Annual Voyager Science Fair in 2376, Naomi Wildman programmed an impressive model of her father's homeworld, including its geophysical and atmospheric conditions. In her model, she programmed a massive storm system over the Arpasian Range, which is known for high winds and hail. (VOY: "Child's Play")
- In "The Voyager Conspiracy", Seven of Nine stated that "the Ktarians were officially with the Federation, but they sympathized with the Maquis." This makes it unclear as to whether Ktaris is a member planet of the Federation or merely allied.
Chakotay once mentioned that Ktaris VII was the Ktarian Homeworld. It's possible that there are two different species called Ktarians, one from Ktaris and the other from Ktaria VII. When we first saw "Ktarians" on TNG they are described as a neutral and soverign species which has had very little contact with the Federation and very little is known about them. They later used a virtual reality device, to which every member of the crew became addicted and eventually fell under their control, for the purposes of infiltration and conquest, making them an enemy of the Federation.
In Voyager however, the Ktarians are spoken of very highly and they are clearly a member of the Federation. Tom even states that there are Ktarians living on Earth. Their culture is well known and well liked. Their cuisine is highly desired and their world a favoured vacation spot. A Ktarian even has an antique shop on DS9.(possibly Naomi's father)It seems unlikely that such a radical change could occur in so short a timespan.
There is also the difference in appearance to consider. The Ktarians on TNG had a bulge on either side of their forehead, with a chasm running between them. They also had reddish skin and horizontal slitted pupils. Even though Naomi Wildman is the closest thing we see to a Ktarian on Voyager, she looks human except for the four small horns on her forehead.( she was born with only three) Although the entries on Ktarians and Naomi on this website claim this difference is due to the fact that she is a hybrid, the Doctor stated that Ktarians have exo-cranial ridges running from the middle of their foreheads over to the back of their heads, as well as scales on their mamory glands, and perhaps other parts of their bodies.
Based on this information, it seems likely that there are two species called Ktarians. Those from Ktaris are the ones spoken of on Voyager and are a beloved member of the Federation, where as the ones we saw on TNG are from Ktaria VII. They are not part of the Federation, and very little is known of them.