Dante's Hell is a cone driven into the Earth beneath Jerusalem. Its point is the center of the world, and every circle is measured as distance from God.
The first circle holds no criminals. Limbo keeps the good who lived before Christ or died unbaptized. Virgil says plainly “they sinned not” (IV.34). Their only punishment is what they lack:
Each circle down is a further turning away. At the bottom there is no fire at all. The worst traitors are sealed in ice, frozen by the wind of Lucifer's wings (XXXIV.46-52), as far from warmth and light as anything can be.
Every soul, guardian and landmark here is cited by canto and line. Where Dante gives no measurement, the proportions follow Renaissance reconstructions.