Gridding is the process by which a continuous, regularly-spaced array of values can be created from irregularly-spaced or scattered XYZ points. What this means is that, rather than having to drill boreholes every 5 feet or 100 feet to determine the elevation of a particular formation at any particular point, you can instead use the computer to extrapolate the elevation based on known depths from borings you already have.
Obviously, the more known points you enter into the program, the more accurate the extrapolation is likely to be. Note that this process is called "grid modeling" not "reality".
In RockWorks, you can select from a number of methods or algorithms which all fill in the blanks slightly differently. You can adjust the density of the grid model (lots of extrapolated points or few).
