Gravity is the automatic vertical acceleration that varies from map to map. Gravity mostly pushes mice downwards, except in map 81, in which gravity is reversed until 1:30, sending mice upwards. Most maps have the same gravity. However, in some maps gravity has been reduced to allow mice to jump higher.
Gravity is a factor in all maps, although in most maps gravity is always in the down direction and with a standard strength. The default gravity amount for maps is 8. Many user-generated maps also utilize gravity changes.
This map will turn its gravity upside-down (-8 gravity measures) if the timer is into 10 seconds. Thus, the shaman must make a roof in the duration of the 10 seconds in order to avoid all the mice dying.
This map has a lighter gravity than usual, specifically 5 amounts of gravity. A reasonable answer for this is so that the mice can get to the cheese more easily and that it's a collision map.
Gravity can be adjusted in the map editor by going to Map Settings and changing the amount of gravity. Adding a - sign to a number will make the gravity go upwards.
The XML tag for gravity is G, which also includes wind. Inside the quotations, the second number is to represent gravity. The tag is normally placed at the beginning of the XML, between <C><P and /><Z><S.
<C><P G="0,-10" /><Z><S /><D /><O /></Z></C>