There is a huge amount of world building involved with this map and I'm afraid I can only write a few points here lest this text becomes an all out fanfiction ;)
On the small island on the sandbank called "Galloper Sand" in the southeastern corner of the map is a tower originally built as a weather station by pegasi (in a region too windy for cloud based architecture to be an option) and since the last pony-griffon war (27 years before the events of our RPG) held by griffons. The Treaty of Trottingham that ended the war imposed some harsh sanctions on the island. These include a ban of food importation from Equestria, the prohibition of pegasi weather control (most pegasi have therefore left the island), the payment of a quarter of the storehouses' contents (and obligation to store everything there) in the first week after harvest month and the prospect of the island getting legally annexed by the Griffons if ever the permanent garrison in the tower exceeds the pony population of the island. These points naturally have a strong impact on everyone living there.
To the north of the tower there is a crater of a meteor impact right amidst the sea and kept dry by a magical sphere apparently created by the inhabitant of a tiny cabin within the crater. I cannot tell too much about her without it being spoilers for the players in the group, but it has been pointed out already that technically that creater constitutes an independent country of its own being neither part of Equestria (to which the Griffish Isles belong) nor to the tiny island annexed by the griffon kingdom.
South of the Horseshoe Square (so named for its shape) in the town center you can see the Sheriff's Keep where Twihorn Shining, the sheriff and governeur of the Griffish Isles by the grace of the royal sisters resides. It is not exactly a castle, but the closest thing to one that can be found on the Griffish isles.
Opposite the Keep is the Big Barel Tavern. Indeed it looks like a giant barrel half burried in the ground and it was mostly put together by planks of ships destroyed or damaged beyond repair in the battle of the Galloper Sand respectively the storm that struck late on the third day of the battle. The Big Barrel Tavern is the social center of the town and it is there that the players of the group learned that their bits aren't going to buy them anything on the Griffish Isles. With most of the gold Equestrian coins are made of (and a lot of other metals for that matter) comming from the Griffish Isles regular currency is deemed worthless on the Griffish Isles in our game setting. In the special situation of the Griffish Isles being helpful within the community and contributing to make everything work has developed into a kind of social currency. Our players will have to make themselves helpfull to earn their meals there.
On the western Side of the river Trot running through the town is the craftspony quarter of the town including Little Brown's sawmill, Brownie Bess' blacksmith shp and Steady Bites brewery.
There are many empty houses in the eastern part of the town since many of the pegasi who left the island after they were no longer allowed to do their job as weatherponies used to life there. So at least it was not difficult for the players of our group to find a place to stay (they only had to register it with the townguard).
In the southeastern corner of the town is the Lunatower, a lighthouse illuminated by crystals with the magic of Sir Rich Art of the Sea, the sole crystal pony resident of the town (ever since his ship got destroyed during the battle of the Galloper sand (or more precisely by the very meteor strik that created the crater north of the griffon tower).
In several places there are treadwheel powered water pumps to keep the mine tunnels underneath the town from filling up with soakage. The mines right next to and under the town are no longer active (ore is dug up elsewhere by now), but if the tunnels fill up with water it would endanger the stability of the ground and many of the buildings.
This is about all that I can say at this point without giving spoilers to the players of the group… and I am wondering who might read through this wall of text at all :D
There are alternative versions of the map with and without text on them respectively with and without reduced opacity. In case these maps are helpful to any other pen and paper role play gamers I'm very curious to hear about it and happy to answer possible questions.