Action Screen - Question Texture Mappings

[Haluum]

i need an explanation what does this part of code do:

private function createTerrainTriangles(num:int):void{
locked = true;
_ground = new Vector.<Number>();
var rows:int = num; //number of points per column
var columns:int = num; //new of points per row
var jumpX:Number = 760/(columns-1);
var jumpY:Number = 560/(rows-1);