Raster grids can be downloaded directly from Surfer using the Grids | New Grid | Grid from Server command, or by clicking the Download button in the Open Grid dialog. To download a grid with true elevation values for the Z values, choose a download from a WCS server. If you choose to download a grid from an OSM or WMS server, the Z values in the downloaded grid range from 0 to 1, because these are not true elevation values, but are values assigned by Surfer to represent the colors of the pixels in the downloaded image. Files downloaded from OSM or WMS can be opened as a Base map and viewed as an image. 

Note: Surfer 13 did not support WCS servers. Downloaded grids showed z values in the 0-1 range. Although these are not true elevation values, the grids can still be useful to get an idea for the relative elevation of the area. Note: if you will be downloading grids from a WMS server, you will want to choose a grayscale terrain layer like the ones in the Terrain Data category, since the color in the image reflects the variable that you want the Z value to represent. If you choose a layer that contains something like an aerial image, the colors in the image do not reflect the elevation or any other value. 

Updated December 2021