Terra is a geologically energetic world, with an abundance of small continent-islands separated by a network of narrow seas, the water covering about half the planet's surface. The oceans tend to moderate temperatures on landmasses since so much land is near a coast; the ice caps (which cover multiple islands on independent tectonic plates) develop channels in the summers of a few years every century, and no large, sandy deserts exist, though deforestation or storms have reduced several smaller islands (there are an abundance of these not maked on the map) to stony wastes. The map below gives general descriptions of the ecology types on each significant island.
The Terran year is 370.5 days, with a leap day required every other year in its nations' calendars. The day is slightly shorter than Earth's, so that years match fairly well. Its sun is an average yellow main-sequence star in the middle of its life span. The skies of Terra boast four visible planets, two inside Terra's orbit and two beyond, in addition to a complement of stars rich enough to provide Terran astrologers with a wide variety of constellations (though no convenient pole star) and a misty galactic band to inspire mythmaking.
Two moons orbit the planet, locked directly opposite each other, so there is rarely a moment of night without a moon in the sky and their combined gravitational pull results in some impressive tides. Their roughly eight-day cycle defines the Tomosic week. One moon is a silvery-white orb, tide-locked in place with familiar markings, with a silica crust that looks like our own; the other is an irregularly round, tumbling ellipsoid of iron oxides in reds and browns.
The Red Moon is inhabited! Construction and roads of some dark material are clearly visible from Terra during part of the moon's rotation. The distance and lack of intervening atmosphere, however, have thus far defeated the most powerful or skillful attempts at examination by magic (and the telescope has not been invented), whether directly or by conjured assistant. Attempts to teleport kill the enterprising mages or their test subjects; explosive decompression will do that(the moon has no atmosphere), but the Tomosics don't know that's the cause, so the moon has developed a reputation, enforced by its foreboding appearance, as the abode of some great evil. Nights when it is full are considered unlucky in Tomos, especially by the countryfolk.
Terra has access to a collection of elementally-pure planes the people of Tomos have dubbed the Elemental Complex, usually shortened to just the Complex. The nation of Tomos has established permanent gates to several, and much industry involves them, despite the difficult conditions of maintaining a human presence in some of the most useful. A minor amount of trade and diplomatic contact involves an intelligent race native to the plane of Water, while the Terran afterlives are distributed across the major elemental planes.
Though the Gate College of magic is highly developed, Terran research interest has mostly focused on accessing various elemental planes. Versions of "elemental" planes that, like Terra, partake of all four of the classical elements, have been posited, and the spells technically work, but difficulties of exploration have limited work in this area. No "alternate Terras", either inhabited or even suitable for colonization, have yet been found.
The Complex is vastly expanded in other sections of this setting, currently still being drafted. Here is a bare-bones summary of the known planes.
In the Infinite Worlds setting, Terra's Quantum level is best left up to the GM; of course, Quantum 6 or 7 offers the opportunity for Homeline and Centrum to observe and perhaps conflict on Terra (though its magic would, for the moment, more likely keep it off limits), while Quantum 1 or 2 would put it entirely out of reach of both those worlds with their present technology.
The elemental planes are a different matter entirely; these could simply be part of a pocket multiverse that surrounds Terra, or the portions accessed and developed could be part of the Astral plane of Cabal cosmology. "Terra"-planes, partaking of all four elements, behave more like natural worlds, but for some reason actually working the spells runs into difficulties; Tomosic mages may be trying to adapt a limited Plane Shift spell that reaches elemental planes without the ability to jump planes in full generality.