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Vector Formats

Contents


Background

  • Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon(s), which are all based upon mathematical equations, to represent images in computer graphics. [From Wikipedia: Vector graphics]
  • Vector Formats and Raster and Grid Formats together constitute the subject materials for Geographic Information Systems.
  • Used here, the term vector is not to be confused with the earth science terms "current vector(s)" and "wind vector(s)" referring to physical or geometric vectors of motion.
    • This gets even more confusing when it is necessary to represent currents or winds on a map, using primitives that draw the requisite arrows. These arrows are, in effect, vector graphic representations of physical vectors.

Line Formats

Line formats do nothing more than draw lines on a map, such as coastlines or political boundaries.

Ungenerate (UNG)

The UNG format is used by ESRI software to deconstruct shapes into simple lines, usually for purposes of export. This example shows the 3rd and 4th segments of a much longer file for the national boundary of Namibia. 

3
16.479476,-28.629042 
16.480063,-28.629628 
16.480650,-28.629628 
16.481236,-28.629042  
16.481236,-28.627575 
16.480943,-28.626988 
16.479476,-28.628455 
16.479476,-28.629042 
END 
4 
16.474489,-28.628455
16.475076,-28.628748 
16.475663,-28.628748 
16.476249,-28.628455 
16.475956,-28.627868   
16.475076,-28.627868 
16.474489,-28.628455 
END


GEBCO ASCII

The General Bathymetric Chart of the Oceans Digital Atlas has an ASCII export utility for coastlines and bathymetry contours. One option (although it is not identified as such) is BASED ON THE OLD GF3 format, developed mainly by the European marine community in the 1980's within a family of precedent-setting standards. In GF3 latitude always precedes longitude.

Surfer Blanking/Boundary Line (BLN)

The BLN format is used by the Surfer gridding and contouring program to draw simple boundary lines, or to blank areas that should not have grid values or contour lines. This example is the first few lines of a 385-line segment that draws the boundary of Ethiopia. If used as a blanking file, it would blank the area inside the polygon, as indicated by the "1" in the first line; a "0" would direct blanking everything outside the same polygon. 

385,1,"Ethiopia",""
36.591827,14.193720
36.579544,14.316048
36.619656,14.279283
36.658218,14.295569
36.702435,14.284711
36.735542,14.295569
36.774113,14.295569
36.829369,14.300995
36.906624,14.295569
36.950779,14.284711
36.950779,14.268429
36.978302,14.241290
37.028034,14.252145
37.088718,14.279283
37.110752,14.355270


Plotter Formats

Plotter formats are also sometimes called "List Formats" because essentially they consist of long lists of objects to draw sequentially on a map or screen.

Data Interchange Format (DXF)

DXF was developed by AutoCAD and is still copyrighted. It is widely used throughout the GIS community as an exchange format between systems that cannot read each other's native formats. This example is a small portion of a file that draws the 400-m depth contour offshore Namibia. DXF files are extremely confusing to "read" because they have few easily seen anchor points where you can begin reading a sequence. 

  0
SECTION
 2
HEADER
 9
$ACADVER
 1
AC1006
 0
ENDSEC
 0
SECTION
 2
TABLES
 0
TABLE
 2
LTYPE
70
16
 0
LTYPE
 2
CONTINUOUS
70
64
 3
GS Solid
72
65
73
0
40
0.00116550116550052
 0
LTYPE
 2
GSDASHED
70
64
 3
GS Internal Dash
72
65
73
2
40
1.74941724941725
49
1.16666666666667
49
-0.583916083916083
 0
LTYPE
 2
GSDOTTED
70
64
 3
GS Internal Dot
72
65
73
2
40
0.583916083916083
49
0.00116550116550052
49
-0.583916083916083


Hewlett-Packard Graphics Language (HPGL)

HPGL was developed for plotters, and quickly became an industry standard. The freeware program IrfanView can apparently still convert HPGL to other formats if you have a legacy file to deal with. See the excellent example on the Wikipedia DXF page, cited below. There is a short, simple example of an HPGL file at the HPGL reference below.

Geographic Information System (GIS) Formats

Some of the above formats can be read by GIS systems, but only as ancillary or exchange data. The true GIS vector formats are these below:

Shapefile Format (SHP)

  • The ESRI shapefile (see documentation link below) is a popular geospatial vector data format for geographic information systems software. It is developed and regulated by ESRI as a (mostly) open specification for data interoperability among ESRI and other software products. [From Wikipedia: Shapefile]
  • Although the name seems to indicate one file and one format, in fact a "shapefile" consists of a group of files with the same filename, but different extensions and different internal formats. Shapes include these components:
    • Main shape *.SHP
    • Database *.DBF
    • Index *.SHX
    • Several other completely optional components, depending on the contents of the shape
  • As a general rule, all programs that recognize shapefiles simply need to be "pointed to" the *.SHP file and they will automatically also use the associated other files.
  • Shapefiles are often delivered from Web sources as E00 compressed files that must be uncompressed with the Import71 program.
  • Available files:

Coverage Format

The ESRI coverage format (see documentation link below) is an older format that can accomodate both vectors and rasters. Apparently it can accomodate about 15 different types of mapping concepts, corresponding exactly to the E00 compression format, also developed by ESRI. Thus coverages usualloy consist of numerous separate files when they are uncompressed. Coverages are often associated with the somewhat dated ArcInfo software versions from ESRI, and there are indications that both are slowly losing importance in the GIS field.

Vector Product Format (VPF)

The VPF (see documentation link below) is a robust GIS format developed by the US military in cooperation with other national defense agencies. Although many of its products are restricted or of lesser importance to oceanographers, Vector Map (see links below) is widely used around the world. The VPF format is based on physical mapping relationships specified by very large physical layouts of files and folders.

KML used for Vectors

Additional Resources


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Information about this article

Short title: Vector Formats

Description: Files containing digital representations of geometric forms, such as points, lines, curves, and shapes or polygon(s), which are all based upon mathematical equations, to represent images in computer graphics. An essential input to geographic information systems.

Expertise level: beginner

Author: Greg Reed

Approval status: approved

Approved by: Greg Reed

Last change: 2012-1-13

Subsection of: Marine Data Format Types

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