Although it was once much larger, as of the year 169 of the Fifth Age, the Gnome Empire consists mostly of two settlements; the Tree Gnome Stronghold (northwest of Ardougne) and Tree Gnome Village (northwest of Yanille).
The map provided, shows the current Gnome Empire; the red area represents the Tree Gnome Stronghold; blue shows Tree Gnome Village; green is Hazelmere's house and the brown region is the gnome ship yard on the island of Karamja.
The Gnome Empire was first established during the First Age, but has changed in nature and leadership many times since. It was, at first, on good terms with the elven nation of Tirannwn, but was destroyed during the God Wars.
The gnomes later resurfaced during the Fourth Age, at which point they re-established their largest settlements; the Tree Gnome Stronghold and Tree Gnome Village. After the elves were forced to leave the region in 1930 to fight in the Elven Civil War, the Gnome Empire extended to cover most of what is now Kandarin, although the humans of Ardougne were an exception.
Some time after the Battle of Atarisundri, the Empire began to weaken under a destabilised government and the soldiers of the Mahjarrat General Khazard. By the early Fifth Age, the Empire has shrunk considerably, primarily to human settlers and attacks suffered by Khazard's Army. This largely contributed to Gnome Empire splitting into two.
Today, the Gnome Empire remains a powerful kingdom, but remains comparatively small geographically to its height.