A floating point number specifying an amount.
For backwards compatibility, MapGenSizes can also be specified as a string, which will be converted to a number (when queried, a number will always be returned).
The map generation algorithm officially supports the range of values the in-game map generation screen shows (specifically 0 and values from 1/6 to 6). Values outside this range are not guaranteed to work as expected.
float | "none" | "very-low" | "very-small" | "very-poor" | "low" | "small" | "poor" | "normal" | "medium" | "regular" | "high" | "big" | "good" | "very-high" | "very-big" | "very-good"