Import Overlay Coordinates The Import Overlay Coordinates displays the standard Windows Open dialog box. Here you specify the name of a text file that contains overlay data in an (x, y, z) format. Each line of the input file must contain three points, the x and y location of a cell along with a z value of an overlay, such as initial head or bottom elevation. A comma, blank space, or tab character must separate the x, y and z values. Graphic Groundwater ignores the first two values (the x and y coordinates) and imports the last value (z) into the current overlay, starting with the first cell and working first along columns then along rows until the grid is filled or until the end of the input file. Many graphics programs provide far better interpolation routines that those included in Graphic Groundwater. These programs often export data in an (x,y,z) format. You can use these programs to interpolate the z values for a model, export the data, then import the z values into a Graphic Groundwater overlay. Consult Chapter 4 for more information on exporting data.