The Lunar Empire rules somewhere around 410,000 square km, including the Heartlands, West Reaches, and Provinces. That’s about the same size as Iraq or a little larger than the state of California. It has an average of 21 people per square km, but includes very densely settled areas and many far less settled areas.
The Kralorelan Empire is even bigger at roughly around 625,000 square km. That’s bigger than the Ukraine or smaller than Texas, but the country I find most useful to get a feel for its size is Chile. Kralorela is a relatively narrow arable band of land, islands, and shallows seas no more than 500 km wide, between the high Shan Shan mountains and Kahar’s Sea. It extends some 1250 km from the tropical forests of Fethlon to the snowy reaches of Ignorance. It has an average of about 15 people per square km, but like the Lunar Empire, it includes very densely populated areas and vast areas of near wilderness.
Much smaller are the kingdoms of Seshnela, the Holy Country, and Loskalm. Seshnela is the largest of the three at somewhere around 89,000 km square (now that Nolos and Pasos have been conquered). That puts it at around the size of Portugal or Indiana. It has about 32 people per square kilometer.
The Holy Country is about 60,000 km square. That’s about the size of West Virginia, Latvia or Lithuania. But less than 40,000 km square is land – about the size of Denmark. As a result, it is the most densely populated at 80 people per square kilometer (on land).
Loskalm is the smallest of the large polities is only about 56,000 km square. It is densely populated at about 57 people per square km.
Some people complain that Glorantha is too small, which I find complete nonsense. It is the size that it is. Use the smaller scale to your advantage. It is only 800 km from Boldhome to Glamour. It is less than 2000 km from Boldhome to Sog City. Let your adventures explore if they are so inclined.
A lot of folk imagine these little polities to be hermetically sealed, which of course they can’t be at this scale.
Many people in the pre-modern world traveled far further than the “most people don’t go beyond the next village” trope.
It is perfectly reasonable to imagine Sartarites traveling to Handra City some 800 km away. We know some Sartarites accompanied Argrath on his circumnavigation of the Homeward Ocean. Similarly, we know that Lunar merchants make their way to Sog City and to the Kingdom of Ignorance.
Do most people travel this much? Of course not. But many Sartarites might have kin in New Pavis or Nochet, have a friend that has been to Furthest, Filichet, or Mirin’s Cross, or have a relative who traveled as far as the Nimistori or to Talastar.
Remember that from atop the Quivin Mountains, you can clearly see all of Sartar. Not just Old Sartar, but the Far Place, Upland Marsh, Beast Valley, the Stinking Forest, Snakepipe Hollow, Skyfall Lake, Vale of Flowers, Greatway, Traders Valley, and the Dragonspine. Heck, you’d be able to see much of Tarsh pretty easily, except that Kerofin and the Dragonspine are in the way.