Assuming you're using Dragon, take a look in the text file "unevenly.txt" and you'll see something like this:
Code:
//Mod11 Stormcrow
//**************************************************************************************
//Unevenly 1.03.62
//Syntax :
//[Source Group] [Frequency] [Left] [Top] [Right] [Bottom] [Altitude Random Addition from 1 to 1000]
////***************************************************************************************
06 1000 0000 0000 6143 4095 005
This is where you can adjust how bumpy a particular terrain will be. The one line that's not commented out tells Dragon to make terrain group 06 (probably grass in the default) bumpy 1000 (100.0%) of the time in the area from (0000,0000) to (6143,4095) (the entire map0.mul size, pre-ML) by adding a random amount (up to 005) to each tile's altitude.