Issue 64

Using Map Projections in Surfer 10

Map projection support is a very powerful new feature in Surfer 10. It allows you to combine data (data, grid and base map files) from different coordinate systems, and convert that data to a new coordinate system for the map to display. It saves you time and effort since you don’t have to do this conversion separately in a different program before using the data in Surfer. For example, you could create a contour map from a grid file in State Plane coordinates, add a post map layer using data in lat/long coordinates, and display the map in any coordinate system you wish.

When Do I Use Coordinate Systems?
You do not always need to set the coordinate system for the map layers or the map. You only need to specify the coordinate systems for the map layers and map if:

1. You load data in one coordinate system (i.e. State Plane 1983 – South Carolina) and want to display the map in another coordinate system (i.e. Lat/Long).
2. You want to create map layers from data that are in multiple coordinate systems, (i.e. one SHP file in State Plane, another in UTM, or another in Lat/Long) and want them to all overlay correctly in the same map.
3. You want to create a map, and export it to a file (such as a SHP or GeoTIFF) and retain the coordinate system information with the exported file.

When a map layer is selected, the Coordinate System tab in the
Property Manager will have a Set button. Set the source
coordinate system for the data file used to create the layer.

Maps
After the coordinate system is set for the map layers, you have the option of changing the coordinate system displayed by the map. This is the target coordinate system. When you select Map in the Object Manager, the Coordinate System tab in the Property Manager shows the target coordinate system that the map will actually be displayed in. Click the Change button to change or convert the coordinate system of the map to any coordinate system you want. When you change the coordinate system for the map, all map layers will be converted from their source coordinate system to this target coordinate system for display purposes.

When you select Map in the Object Manager,
the Coordinate System tab in the Property Manager will have a
Change button. Change the target coordinate system for the
map to be whatever you want.

Step-by-Step Example
We can walk through this in a step-by-step example, using the files located in the Surfer Samples folder in the installation directory.

1. Go to Map | New | Shaded Relief Map.
2. Select Diablo.grd and click Open. The map is created
3. Select the Shaded Relief Map layer in the Object Manager.
4. In the Property Manager, go to the Coordinate System tab. See that the coordinate system information is automatically entered for this map, and is set to State Plane 1927 – California III (Meters). This is because the coordinate system information for the grid file we selected is already stored in a reference file in the Samples folder.


A shaded relief map is created in State Plane coordinates.


5. Go to Map | Add | Post Layer.
6. Select Diablo Example.dat and click Open.
7. This data file had no reference information associated with it, and the coordinates are in a different coordinate system than the grid file (they are in UTM, not State Plane), so a warning appears asking us if we want to adjust the map limits. Click No. We will create the post layer first, then assign the coordinate system to it.
8. Select the Post layer in the Object Manager.
9. In the Property Manager, go to the Coordinate System tab. Since the data file did not have any referencing information associated with it, the coordinate system is set to Unreferenced local system.
10. Click the Set button.
11. This data set happens to be in the UTM NAD83 Zone 10N coordinate system. In the Assign Coordinate System dialog, select Predefined | Projected Systems | UTM | North America | North America NAD83 UTM zone 10N.


Select the coordinate system for the Post layer in the
Assign Coordinate System dialog.

12. If I you think you would have a need for this coordinate system in the future, click the Add to Favorites button so this coordinate system will be added to your Favorites list for easy access in the future.
13. Click OK and the coordinate system is applied to the post map layer. You can now see the post symbols on top of the shaded relief map.


Once the correct coordinate system is set for the Post layer, you can see the post symbols over
the Shaded Relief Map layer.

14. This map combines the grid file in State Plane coordinates with the post map in UTM coordinates, and displays it in State Plane coordinates. Let’s now convert the map coordinate system so that it is displayed in latitude and longitude coordinates. Select Map in the Object Manager.
15. In the Property Manager, go to the Coordinate System tab. It currently shows State Plane 1927 – California III (Meters) as the coordinate system for the map.
16. Click the Change button.
17. Open Predefined | Geographic (lat/lon).
18. Under this heading is a long list of datums. Choose the datum you want for your lat/long data. In most cases, World Geodetic System 1984 (WGS84) is an appropriate datum. Select World Geodetic System 1984.
19. Click the Add to Favorites button if you think you might select this coordinate system in the future.
20. Click OK and Surfer reprojects both layers to the new coordinate system and displays the map in lat/long.


Change the coordinate system of the map to World Geodetic System 1984 to reproject the layers and
display the map in lat/long.

21. Note the individual layers in the map retain their original projection. If you click on the Post layer, you can see it is still set to the UTM coordinates. If you click on the Shaded Relief Map layer, you can see it is still set to the State Plane coordinates.