Graphics Reference
In-Depth Information
•
INT
—This is used for an integer. Typically, you use
DOUBLE
if you
are using a number.
INT
is used for lookup codes such as a shape.
GDF supports different node shapes (called
style
) such as circles,
squares, and images where the code
1
corresponds to a square,
2
is a
circle, and so on. Note that not all graph software supports the use of
different shapes.
The links section is similar to the nodes section:
•
edgedef>
—The header row starts with the keyword
edgedef>
to
clearly mark the start of the nodes section.
•
NodeA
,
NodeB
columns
—The first two columns define the links. For
directed graphs, the first column indicates the source node, and the
second column indicates the destination node.
•
weight
—An optional
weight
column with numeric values defines the
thickness of the links connecting nodes. This is very effective for
indicating the strength of the relationship. Some caution is required
when setting weights in the source data—some software will not handle
negative weights; some software will truncate large numbers, and some
will not. Gephi, for example, may display a massive arrow larger than
the entire graph, thus obscuring everything for a large value. A safe
approach is to normalize the
weight
data to the range of 1-10 or 1-50
for the first time the file is created and iteratively experiment with the
visualization software.
•
Other link columns
—Additional columns can be added, such as
labelvisibility
,
color
,
directed
, and so on. The use of the
directed
column can be particularly useful if the graph has a mix of
both directed and undirected links. Otherwise, if the graph has links of
all one type (directed or undirected), most graph software provides a
simple checkbox to declare all links as directed or undirected.
GDF files can be easily edited with a spreadsheet. To export a GDF file from
a spreadsheet, save it as a CSV file, then rename the extension from
.csv
to
.gdf
.
Other Node-and-Link File Formats
Many other file formats exist. You may want to use a more structured file
format, such as GML or GraphML. These formats potentially offer more
