As others have said, each realm has every type of biome, it gets weird as you get farther (either corebound or edgebound, I can't remember) cause' those areas are more affected by the realm's magic. A good example is Aqshy, there are entire oceans in the Realm of Fire, with major port cities like Anvilgard. There are normal parts of the realms, and it probably wouldn't be a stretch to say a normal part of Aqshy wouldn't be too far off from a normal part of Azyr or a normal part of Ghyran.
Each realm spans the size of its own planet, basically. You could think of Aqshy like earth if everything below the equator stayed the same, everything between the equator rained fire occasionally but was generally the same if much hotter, and the North Pole was a shoggoth made of flame.