Export Overlay Coordinates The Export Overlay Coordinates displays the standard Windows Save As dialog box. Here you specify the name of a text file that will hold the grid coordinates for the current overlay (x, y, z). The file can then be used outside of Graphic Groundwater with any program capable of reading a text file. The Save As dialog box allows you to choose your origin, the lower left or the upper left corner of the grid. Graphic Groundwater calculates the coordinates in the center of a cell based on your choice of origin. MODFLOW uses an upper left origin. Other programs, such as GPTRAC, part of the WHAEM package from the USEPA, use a lower left origin. Type in the name of the file. Graphic Groundwater will add the txt extension. Consult Chapter 4 for more information on exporting data.