Surfer reads the x, y, z file and converts it to an internal grid file. This file has a . grd extension. It will open a dialog box. List your directory, and choose file sites.txt , and bring them to Surfer. Now you are ready to interpolate the data.
Interpolation is the most important part of the elevation modeling process.
You can choose from different interpolation methods and you can also adjust some variables to influence the interpolation. Some interpolation methods are good for data which have a lot of data points and the region is sampled homogeneously. It takes a lot of experience to determine what kind of interpolation method to use for particular problem. And, assign the name of the grid you are going to compute. Remember, that you will use this grid three times to produce three different maps.