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You can create a map showing vectors either by:

1.       Creating a post map with a vector at each particular XY location using magnitude and direction data. The process will depend on if you already have the magnitude and direction data for the data points.

a.       You can have Surfer calculate the magnitude and direction data (requires you have Z data for each XY point).

b.      You already have the magnitude and direction data in a worksheet.

2.       Gridding the data and creating a vector map.

1a. Post Map from XYZ data file, with Surfer calculating the magnitude and direction:

Calculate the direction and magnitude at each data point:

1.       If you do not already have a grid of the XYZ data for your points, go to Grid | Data, select the data file and click Open.  Select the gridding parameters (or accept the defaults) and click OK to create the grid.

2.       Go to Grid | Calculus.

3.       Select the original grid and click Open.

4.       Select Terrain Modeling | Terrain Slope. This will be the slope value or slope amount.

5.       Click OK. This will create a grid file of the slope.

6.       Go to Grid | Calculus again.

7.       Select the original grid and click Open.

8.       Select Terrain Modeling | Terrain Aspect. This will be the slope direction.

9.       Click OK. This will create a grid file of the angle of the steepest slope.

10.   Go to File | Open, select the data file that has the XYZ coordinates for those point locations and click Open. This will open in the Surfer worksheet.

11.   Replace all the Z values in the Z column with 0. You can do this by highlighting the Z data column, going to Data | Transform and using the equation C=0 (where C is the column letter of the Z data column).

12.   Go to File | Save As to save the data to a new data file (you probably don’t want to overwrite the original data).

13.   Go to File | Close to close the data file.

14.   Go to Grid | Residuals.

15.   Select the Terrain Slope grid file and click Open.

16.   Select the data file with the XY0 coordinates for those point locations and click Open.

17.   In the Grid Residuals dialog, specify the X, Y and Z data columns and choose to store the residuals in Column D (or the first blank column).

18.   Click OK.

19.   The worksheet is opened. If you have title headers for the data, change the title for the Residuals column to be Slope Amount. The data is also the negative of the “true” data, so highlight the slope amount column and go to Data | Transform. Use the function D=-D (where D is the letter of the column with the slope amount data), change the First row to 2 if you have header data, and click OK.

20.   Go to File | Save and save the file.

21.   Go to File | Close and close the file.

22.   Go to Grid | Residuals again.

23.   Select the Terrain Aspect grid file and click Open.

24.   Select the data file saved above in Step 20 (with the X, Y, Z and Slope Amount) and click Open.

25.   In the Grid Residuals dialog, specify the X, Y and Z data columns and choose to store the residuals in Column E (or the first blank column).

26.   Click OK.

27.   The worksheet is opened. If you have title headers for the data, change the title for the Residuals column to be Slope Direction. The data is also the negative of the “true” data. This is OK for how we are going to use this data, so we will not change it.

28.   Go to File | Save and save the file.

Create the post map

1.       Now you can create a post map to display the data. Go to Map | New | Post Map (or Map | Add | Post Layer to add this to another map layer).

2.       Select the DAT file saved above and click Open.

3.       Set the X and Y Coord columns, and set the Angle to be the column with the Slope Direction.

4.       Change the Default Symbol to an arrow by clicking on the Default Symbol button. You can keep the Symbol Set set to Default Symbols and choose an arrow symbol (like symbol Number 62) and click OK.

5.       In the Symbol Size section, select the radio button next to Proportional.

6.      Click the Scaling button.

7.       Set the Worksheeet Column Containing Height to the Slope Amount column. Change the Symbol Height values if want and click OK.

8.       Click OK and the gradient vectors are shown at each data point location.

1b. Post Map from XY data file with known magnitude and direction:

1.     Combine the magnitude and direction information into a single file with your XY point location coordinates.

2.     Create a post map with the Map | New | Post Map menu command, select your data file and click Open.

3.     Double-click on the post map to display the Post Properties dialog box, click on the General tab and change the Angle to the column containing the direction information. Note:  Surfer measures the direction in a counter-clockwise direction, and you can use the worksheet to multiply the direction column by -1 to reverse the direction.

4.     To specify the size of the symbol, go to the General tab and change the Symbol Size to Proportional and click on the Scaling button to specify the minimum and maximum symbol size for the designated data value.

5.     Change the Default Symbol by going to the General tab and clicking on the Default Symbol button to display the Symbol Properties dialog, click on the Symbol Set, specify a Symbol Set.  Some recommended symbols include:

·         GSI Default Symbols 60 and 61 plot the center of the arrow at that location. 

·         GSI Default Symbols 62 and 63 plot the base of the arrow at the XY coordinate.

·         For wind arrows, select the GSI Wind Barb Symbols.

2.     Vector Map from GRD file:

Surfer can create vector plots from a grid file, or from two grid files individually containing direction and magnitude information by using the Map | New | 1-Grid Vector Map or the Map | New | 2-grid Vector Map commands.

The 1-Grid Vector map calculates the slope or gradient direction from the Z values in the GRD file to draw vectors with magnitude and direction properties.  Choose the Map | New | 1-Grid Vector Map menu command, and specify the GRD file name to create the initial map.  Double-click on the map to display the Properties dialog box, click on the Scaling tab, and set the Minimum and Maximum values to the same value for the Shaft Length, Head Length, and Symbol Width.

The 2-Grid Vector map draws vectors based on two grid files containing the X and Y components, or the magnitude and direction components.  Choose the Map | New | 2-Grid Vector Map menu command, and specify the first GRD file name, click Open, then the second GRD file name, and click Open to create the initial map.  Change the Minimum  and Maximum values to the same value as for the 1-Grid Vector map.

See also: How do I grid directional data, such as wind speed and direction?