Area

Heroshi is a small world compared to the Earth. A perfect sphere, its circumference is only about 5000 miles (compared to Earth's nearly 25,000 about the equator). The continents of Heloth and Anherosh both at their widest points measure about 1200 miles across. Sample Distances: Westlamp to Hackport is 550 miles (comparable to Little Rock to Atlanta). 

Structure

From surface to center is 800 miles. The lithosphere of Heroshi reaches about 30 miles in depth, mantle 30 - 440, and the core 440 - 800. On this Cutaway Diagram, Point X is the Dragon's Maw in Heloth and point Y is in the Steel Isles of Anherosh. The path between them is 'Ald Fel (Vilhan's Folly). 

Light and Heat

Heroshi does not rotate around any celestial bodies because it is the only thing that exists in the Prime Material plane. All outside of it is airless, heatless void. The equivalent to our sun, Solarion, which resides in Erhad, projects light during the day, while heat comes from the plane of fire. These planes overlap the material and extend their properties into them. Night comes as a result of Kalnuega, the Sphere of Darkness in Nuegalon.

Celestial Objects

Celestial bodies are objects in the supernal plane of Erhad. Stars are pieces of crystal literally imbedded in the heavens that are a remnant of a shell formerly designed to keep celestials out of the material plane. Moons are liquid spheres controlled by Lunar celestials which influence the tides and used for signs. Planets are not visible from the material plane. They exist in Erhad as spheres of great size that serve as access points for various demiplanes.

Climates

Climates are affected by the elemental planes as well. The influence of the plane of fire is concentrated on the north pole whereas water (cold) is on the south.

Oceans

Heroshi has four oceans, which were discovered by dwarven explorers who set off, one toward each of the cardinal directions, presumably from Muirstone.

Gravity

Gravity is a force invented by Vilhan. In some planes gravity is toward the inside as it is on the material plane while in others it is toward the outside. Yet others have subjective gravity (Nuegalon, plane of air), weak gravity (Ethereal Plane) or none at all.