Geology, and the planet
Aside from the planet itself, one major difference between the DwrvenWorld and our old Earth is its satellite. The DwarvenWorld has nothing like our erratic and overblown Moon; it has a discreet little satellite, about one third in apparent size, which spins around the planet at the same speed it rotates, so that it is always above the same point of its equator. At least from the lands inhabited by the Arvarii, in which our setting is described, this is the only visible moon. If others exist, they must be on the other side of the planet. The cultural consequences of this fat are remarkable. If there are eclypses on the DwarvenWorld, they all happen close to the equator, and in fixed hours of the day. This does not concern the territories we consider: here eclypses simply never happen; the narrator in need of some device for ill omens will have to turn its fancy to some other natural phenomenon (a volcanic eruption, the passage of a comet, an invasion of toads).
ost fantasy settings, with the noticeable exception of TSR's Dark Sun, assume that the planet your characters live on is more or less our old, reassuring Earth, with one big Moon spinning around it in 28 days and so forth. It is not so with the DwarvenWorld. Here the planet itself is somewhat different, and not only in how countries are arranged. Its most relevant features will be detailed here.
First of all, the DwarvenWorld is not as big as the Earth. Its radius is about 5300 kilometres against the 6400 of our planet, which means that if you decided to sail all the way around it, you'd save a good month.
In spite of this lack in size, the gravity on the surface of the DwarvenWorld is about the same as here; this apparently absurd fact is explained by its density, which is by far higher: heavy metals, like platinum, gold and iridium are by far more common. This has a first practical implication, that gold is not as precious as one would expect: where on our Earth, at the technological level we are considering, a single, large gold piece would suffice to one's needs for months, a couple of days of debauchery for one in Gorhad are more than enough to consume it. Platinum and its kin (osmium, rhodium, etc., which are not recognised as distinct by DwarvenWorlder, anyway, and globally known as "true silver") are even more common than gold, but since they are extremely hard to melt and work, true silver coins and artifacts are very, very precious; they are sold as powder, crystals and needles for a few dimes, however. Silver, on the other hand is worth around ten times less than gold, and is the most commonly used metal in everyday transactions, say if one needs to buy a mug of ale (further specifications shall come in the currency section).
The axle of the planet, also, is more perpendicular to its plane of travel: the continental climate of the DwarvenWorld is therefore much easier to bear, and people live commonly in areas that are thousands of kilometres inland without excessive problems. Onhe drawback of this situation is that northern countries are quite cold all the year through, including the middle of the Summer. And that's quite right, since in fantasy settings the North should always be snowy, regardless of the season.
Tides also never happen. The surface of the sea is simply sloped towards a certain point of the equator, and stays this way; the most skilled navigators are aware of this fact. But, most important of all, it is extremely easy to navigate with the moon: its vertical position (how high it is over the horizon) tells how north one is, while its horizontal position tells how close one is to a certain meridian line. Furthermore, the shade on its surface tells the time of the night. Only the most trained eyes can evaluate these things without the help of particular instruments, but these are not too hard to find: the most common of this is the moon watch, which is simply a metal circlet with wire positioned so to tell the time according to the look of the moon. Much more complicated (and costly) devices are used by marineers to find their way in the open.
As far as the drift of continents is concerned, the continent in which the setting is developed is moving north, parting from the one on which Nebria is, which is moving south. This has no obvious effect on the campaign, but it means that the southern part of the Arvarian continent tends to be covered by plains, and that active volcanos are increasingly more common the more one moves north; volcanic activity is common in northern Clenia and in the Mist Countries. Also, the northern coasts of the continent face a much deeper sea.
A small hot spot is located under the Peak of the Damned, north of Zarvedi, and its effect extend as far as Gorhad; the whole radius is interested by massive geothermal effects, such as hot springs, gaysers and, last but not least, sulphur-loving underlings.