Golden Software Blanking .BLN File Description

Surfer imports and exports Golden Software Blanking Files .BLN.

Golden Software Blanking File .BLN is an ASCII format file used to store geographic information including polygons, polylines, and points. Spatial information is only concerned with the location of objects in space (i.e., their coordinates) and not with their attributes (i.e. line or fill style, marker symbol used, text labels, etc.). Even though the primary use of GS Blanking files is to indicate regions of a grid file to be assigned the NoData value, they can also be used for simple boundaries and decorative illustrations.

File Format

The general format of the file is:


length,flag "Pname 1"





length,flag "Pname 2"






The length value is an integer which indicates the number of X, Y coordinate pairs that follow.


The flag value is 1 if the region inside areas is to be assigned the NoData value and 0 if the region outside areas is to be assigned the NoData value.


Pname is optional and is the name of a primary ID to be associated with the object. The primary ID is used to link the object to external data.

X, Y Coordinates

Following lines contain the actual X, Y coordinate pairs that make up the object. These can be integers or real numbers, and are stored 1 pair per line.

Type of Object

The type of object is determined as follows:

  • If the type/length field is 1, the object is considered a point. One coordinate pair follows.

  • If the type/length field is greater than 1 and the first and last coordinate pairs are equal, the object is considered a simple closed polygon. Otherwise, the object is considered a polyline.


The first ID attribute for all polyline, polygon, and symbol objects are automatically exported to all .BLN files. For contour maps, the elevation is exported as the "STD_ID1" attribute for all polylines in the contour map. If a different attribute other than the first listed attribute for objects is desired, rename the desired attribute to "STD_ID1". This named attribute will be used instead of the first attribute listed on the Info tab. The color, size, symbol shape, width, and other properties are not exported.

Multiple Polygons and Polylines

The sequence may be repeated any number of times within the same file to define multiple polygons and polylines.

Blanking Flag

The blanking flag parameter is used to determine whether the NoData value is assigned inside (1) or outside (0) the polygon. The XY coordinates used in the blanking file are in the same units used for the XY coordinates in the grid file. When creating a .BLN with the Digitize command, the default blanking flag is a 1. If you need to assign NoData values outside the polygon, click Options | NoData Inside Region in the Digitized Coordinates window to clear the NoData Inside Region option.

With breaklines and faults, the blanking flag is not needed and can be left empty.

Optional Z Coordinate

A Z coordinate may be specified after the X and Y coordinates when using a .BLN file for breaklines. The Z value is required for breaklines. Faults do not require a Z coordinate.


This example shows a simple .BLN file, with a single polygon:

5 0

1 1

1 3

4 3

4 1

1 1


This example shows a single complex polygon .BLN file, with an island. Note the 48,99 coordinate pair starts the first polygon (line 2), closes the first polygon (line 8), and closes the entire complex polygon (line 14). The 40,70 coordinate pair starts (line 9) and closes (line 13) the sub-object within the complex polygon. Each sub-object in a complex polygon is followed by the first polygon coordinate pair:

13 0

48 99

52 20

57 19

56 8

29 0

27 71

48 99

40 70

50 60

48 55

34 40

40 70

48 99


The following example defines two breaklines for input into the gridding module:

2, 1

3.0, 4.5, 1.0

0.5, 4.5, 2.0

3, 1

4.5, 0.0, 1.1

8.5, 0.0, 1.2

8.5, 1.5, 1.4


The following example defines one fault for input into the gridding module:

2, 1

1.5, 1.0

7.5, 8.5

Loading a BLN

Use the  File | Open or the Open Data dialog (i.e. Home | New Map | Base, Home | New Map | Post) to load a .BLN file.

Saving a BLN

Use File | Export to save a BLN file from the plot window. BLN files are also created via the Digitize command and various grid operations.

Import Options Dialog

No import options dialog is displayed.

Import Automation Options

No import options are available.

See Also

Blanking File Format

File Format Chart

Creating a Blanking File with the Digitize Command

Golden Software Blanking Export Automation Options

Golden Software Blanking Export Options Dialog

Golden Software Blanking Import Automation Options