When to set the coordinate system for a map or layer in Surfer

Some scenarios where you would want to set or change the coordinate system for the layers or map include:

• If your data sets are in different coordinate systems or units.
  
  In this case, you will want to set the coordinate system for each layer (source coordinates) and the entire map (target coordinate system) so that the data overlays properly. For example: you have a base layer in UTM coordinates and want to overlay it with a contour layer created from a grid file in lat/long coordinates. The coordinate system for the base layer should be set to UTM, the coordinate system for the contour layer should be set to lat/long, and the map could be set to whatever system you want the map to be displayed in.
  
  
• If you want to change the projection or units displayed by the map
  
  In this case, you will want to set the coordinate system for each map layer (source coordinates) and the entire map (target coordinate system) . For example: you have a contour map created from a grid file in UTM coordinates and want to display the map with lat/long coordinates on the axes. The coordinate system for the contour layer should be set to UTM, and the coordinate system for the map should be set to lat/long.  Another example is if you have a grid file in inches and want to display the map in feet or meters.
  
  
• If you want to export the map to a referenced file (i.e. KML, GeoTIFF, etc).
  
  In this case, the coordinate system of the map must be specified so that it can be exported correctly. If all the layers in the map are in the same coordinate system as the map, they do not have to be specified individually - just select Map in the Contents window, click the Coordinate System tab in the Properties window and click the Assign Now button. That will assign the same coordinate system of the map to all the unreferenced layers. 
  
  
• If you want to download an online base or grid layer (Home | Add to Map | Base from Server).
  
  In this case, set the coordinate system of the Map object with the target coordinate system and any layers (i.e. Base or Contour) with their respective source coordinate systems. Setting a coordinate system will allow Surfer to automatically download the image or grid for your map limits while in the Download Online Maps dialog accessed by clicking Home | Add to Map | Base from Server. 

See the articles below for more information:

• Use map layers with different coordinate systems in the same Surfer map 
• Difference between setting the coordinate system for a layer, and changing it for a Map in Surfer 

Updated December 2021