How do I merge two or more GRD or DEM files to create a contour map?
A. Overlay two contour maps to align them by their XY coordinates, or convert the GRD or DEM files to ASCII XYZ DAT, merge them in the worksheet, and regrid. To merge contour maps of different GRD or DEM files, create a separate contour map from each DEM file in the same plot window, select the maps, and choose the Map | Overlay Maps menu. Surfer will align the maps according to their XY coordinates. To merge the GRD or DEM files into a single file, choose the Grid | Convert menu command, specify the GRD or DEM file, and save as an ASCII XYZ DAT file. Repeat for the other GRD or DEM files. Open the first XYZ DAT file in the worksheet, go to a blank row after the end of the file, and choose File | Import to merge the next DEM file. Save the merged data file, close the worksheet, choose the Grid | Data menu in a Plot window, specify the new data file, change the grid spacing to match that of the DEM (30 for 1:24,000), and change the grid method to Nearest Neighbor. Click on the Data tab,