Create a BLN file with multiple polylines in Surfer

Method 1: Draw it in the Plot Window

You can also draw the objects you want over your map and export them to a BLN file. To do this:

1. Select your existing map and click Home | Add to Map | Layer | Empty Base. This will add an empty base map layer, called Base(vector), to your map.
2. Select the new empty Base(vector) map layer in the Contents window
3. Click Features | Insert | Polyline and draw the polyline over the map. You can use the scroll bars on the sides of the window when drawing the polyline. You may want to zoom in a few times so you can see the map clearly.
4. Double click or press ENTER when you are finished to end the polyline. Now the base map layer has one polyline object in it. Draw as many polylines as needed.
5. Press the ESC key on the keyboard to exit draw mode.
6. Turn off the four axes in the Contents window (uncheck them) and any other map layers (ie. a Contours layer) or objects that are not the drawn polylines.
7. Click File | Export.
8. In the Export dialog, choose a location to save the file, give the file a name, and choose to save it as BLN Golden Software Blanking (*.bln).
9. Click Save.
10. In the Export Options dialog, click OK, and the file is created.

Method 2: Digitize from Surfer

It is easy to digitize line segments from an existing map in Surfer (contour, base, etc.).  When creating a BLN file in this manner, the header information is added to the file automatically. To create a BLN file with the Digitize command:

1. Create a map in the plot window, and then select the map. This can be an overlay, although the overlay cannot contain a wireframe or 3D surface, or be tilted at any angle other than 90 degrees.
2. Click Map Tools | Layer Tools | Digitize and the pointer becomes a cross hair.
3. Click the left mouse button in the plot window to write the current coordinates to the Digitized Coordinates editor window. Click on the location for all vertices in the first line.
4. If you wish to create multiple polylines, click in the Digitized Coordinates window and manually insert a blank line. Then click in the plot window on the locations for all the vertices in the next line. 
5. Repeat inserting a space and clicking for each polyline you digitize.
6. When you are finished defining the polyline(s), click File | Save As in the Digitized Coordinates window, and save the file as a BLN file.
   • If the BLN will be used to assign NoData, before saving, click Options and check or uncheck NoData Inside Region as necessary to add the appropriate blanking flag. 
7. Press ESC or choose any tool button to exit digitize mode.
    

Method 3: Create Manually in a Text Editor

You can also simply enter the vertex coordinates for the polylines in a text editor or the Surfer worksheet. This method is best if you have known X,Y values for your line segments. The BLN format is a one-line header followed by a list of XY coordinates for the object. The header is simply the number of data points in the object. Then save the file with a BLN extension.

Below is an example of the proper format for 4 separate 2-point polylines.  The header consists of the number of points in the line.

Note: You can view your BLN file in Surfer using the Home | New Map | Base command.

See also: Create a NoData Polygon or BLN file in Surfer

Updated November 10, 2021