Creating a Contour Map

A contour map is a two dimensional representation of three dimensional data. Contour maps are produced from grid [.GRD] files or USGS DEM files. Grid files contain a regularly spaced array of XYZ data points interpolated from your original data. To create a contour map you must first create a grid [.GRD] file from your XYZ data [.DAT] file. After you have a grid file you can then create the contour map. Alternatively, Surfer will automatically convert a DEM file to the grid file format necessary to create a contour map.

The smoothness of contours on a Surfer contour map is partially a function of the number of X and Y lines in the grid [.GRD] file. When you create a grid file, reducing the number of lines in the X and Y directions can result in more angular contours on your contour map.

Surfer allows you to add color fill between contours. Color fill can be applied to each contour interval manually or you can create a Fill Spectrum by specifying the colors to assign to the Minimum and Maximum contour intervals.

Creating a Contour Map:

1. Create a grid [.GRD] file of your data using the Data command from the Grid menu. Grid files can also be produced from the Function and Math commands.

2. Choose the Contour command from the Map menu and the Open Grid dialog box is displayed prompting you for the name of the grid [.GRD] file or USGS DEM file. Specify the name of the file and click OK. The Contour Map dialog box is displayed.

3. Specify any parameters in the Contour Map dialog box and click OK. A contour map is created from your grid or DEM file.

Specifying Contour Levels

Contour levels are represented as lines of constant Z value on a contour map. When you display the Contour Map dialog box, the contour levels for the map are listed in the Contour Levels group. You can specify the contour levels to use on a map in several ways.

You can automatically assign regularly-spaced contour levels using regular intervals by typing the smallest and largest Z values and the contour interval between adjacent contours. For example, the smallest Z value (the minimum contour level) could be defined as 50, the largest Z value (the maximum contour level) could be 100, and the interval between contours could be 10. In this case contour lines are drawn at Z levels of 50, 60, 70, 80, 90, and 100. If the range of Z values goes beyond the minimum and maximum values you define, the contours outside the range are ignored.

You can assign contour levels by double-clicking the contour value in the Contour Map dialog box and typing the value for the contour level.

To create contour levels at regular intervals:

1. To create the contour levels, double-click the map and the Contour Map dialog box is displayed.

2. To assign evenly spaced contour levels, click the Level button in the Contour Levels group and the Contour Levels dialog box is displayed.

3. Type in the values for the Minimum and Maximum contours, and the Interval value that defines the spacing in Z units between adjacent contour lines.

4. Click the OK button and the Contour Levels list is updated in the Contour Map dialog box. Click OK and the map is displayed with the new levels you specified.

To create contour levels at any user-specified Z value:

1. Double-click the map and the Contour Map dialog box is displayed. In the Contour Levels group, all the contour levels are displayed.

2. Click the Add button to add a contour level midway between the selected level and the next lower level. Clicking the Delete button removes the selected level from the list.

3. When you are through adding or deleting levels, you can double-click the level value for the contour levels in the list, and Enter a new value for the contour level in the Z Level dialog box. Click OK and the Contour Levels list reflects the change.

4. When you are finished defining the contour levels, click OK and the map is displayed with your changes.

Contour Line Attributes

Each contour level can be assigned individual line attributes. You can assign contour line attributes so there is a gradational change (of color, width, or both) from the minimum to maximum contours, or you can assign specific line attributes to individual contour levels.

Gradational colors or widths are assigned by specifying the color or width in the Line Spectrum dialog box. This dialog box allows you to set the attributes for the minimum and maximum contour level. This creates a gradation of colors or widths from the minimum contour line to the maximum. For example, you can assign the color red to the minimum level, and the color blue to the maximum level. The assigned contour line colors gradate from red to blue. If you do not want to display contour lines for a plot you can assign the "invisible" line style to both the minimum and maximum contour levels.

In contrast to contour line color and width, there is no gradational change between line styles (dashed, dotted, etc.) when different styles are assigned to the minimum and maximum contour levels in the Line Spectrum dialog box. In this case, the lower half of the contour lines use the style assigned to the minimum contour level, and the upper half of the contours use the style assigned for the maximum contour level.

You can also assign attributes to individual contour levels by double-clicking the line sample in the Levels group. When you assign line colors manually, you specify the attributes for each individual contour level.

Assigning Line Attributes using a Color Spectrum or Gradational Widths:

1. Double-click the map to display the Contour Map dialog box. Click the Line button in the Contour Levels group and the Line Spectrum dialog box is displayed.

2. Click the Minimum button and the Line Attributes dialog box is displayed. Select the color and/or width you want to assign to the minimum contour level on the map.

3. Click OK in the Line Attributes dialog box and repeat the procedure for the Maximum contour line.

4. Click OK in the Line Spectrum dialog box and you are returned to the Contour Map dialog box. The line colors and widths you specified are shown for the minimum and maximum contour lines, and the intermediate contour lines display gradational colors from the minimum to the maximum. Be aware that some video cards and monitors are not capable of generating smooth gradations from one color to another, so the line spectrum might consist of ranges of one color, resulting in "color zones" rather than a smooth line color spectrum.

5. Click OK in the Contour Map dialog box and the contour map is drawn with a color and/or width spectrum from the minimum to the maximum contour lines.

Assigning Line Attributes to Specific Contour Lines:

1. Double-click the contour map to display the Contour Map dialog box.

2. Double-click the line sample for the contour line you want to modify, and select the line attributes from the Line Attributes dialog box.

3. Click OK in the Line Attributes dialog box and repeat the procedure for all the contour lines you want to change. When you are done, click OK and the map is drawn with the attributes you specified.

Assigning the Same Line Attributes to all Contour Levels:

1. From the Contour Map dialog box, click the Line button in the Color Levels group and the Line Spectrum dialog box is displayed.

2. Click the Minimum Line Attributes button and specify the line attributes you want to use for all the contour lines on the map. Repeat the procedure for the Maximum Line Attributes, specifying the same attributes for the maximum contour lines.

3. Return to the Contour Map dialog box and click OK. The contour map is displayed with the same contour line attributes for all contours on the map.